Since many countries around the world have been focused on banning and discontinuing traditional light sources like incandescent, fluorescent, halogen, and HID sources in favor of LED, I have a strong feeling that within less than 10 years from now, virtually all traditional electric light sources in existence outside of private collections and museums will become unobtainium and too “RARE” to operate every day from a collector’s perspective by that point due to large numbers of NOS lamps and ballasts getting scrapped, recycled, and destroyed due to progressively shrinking supply and demand assuming there will be no alternative to LED lighting.

I wonder when that time will come when virtually all traditional electric light sources that aren’t LED will become unobtainium and mostly confined to private collections and museums.

Impossible to say?, depends when exiting stocks run out, but I think the last one to become unavailable will be HPS lamps?
It’s also impossible to say whether existing stocks will even be binned as for lack of demand?, I doubt people are going to keep stuff just for a handful of lighting enthusiasts around the world?

Rectified fluorescents were made obsolete around 1960's, but still (!) manages to surface up sometimes. I am even not talking about 1910's carbon arc lamps!

I think one big difference compared to obsolete lamps of previous decades is that most of those that have been phased out within last 20 years have been used in vast numbers. I would be far more concerned about finding a fixture to use them than light sources.

Like how 50w and 75w mercury lamps are plentiful on eBay, but the fixtures and ballasts for them are very rare.

Yeah, even common stuff that was discontinued 28 years ago such as F40CW lamps still show up from time to time.

Yeah 50w and 75w MV ballasts are rare enough, much less an entire fixture. For now at least it seems HPS lamps and 4ft T8 fluorescents are the most common stragglers for conventional lamp types here. Apparently some places still use decent numbers of incandescent traffic signals too which explains why the lamps for them still seem to be produced in small quantities. 

Seeing all that - I am also trying to get some ballasts (magnetic and pre programmed start electronic) for my collection of fluorescents and discharge lighting. Also making sure that I'll have access to B22< E27, B15 and E14 fixtures that can handle the wattages of the non LED lighting

One definite benefit to this situation is that the prices of many types of lamp that have only recently gone obsolete, have gone down a LOT. The professional consumers know they will either go out of production soon, or have already gone out of production, so the remaining stock is often sold off for pennies on the dollar with the professional market very rapidly having switched over to LED, reducing demand for the current stuff.

I can get SON lamps for like 2 euro a piece with a bit of luck, 6 with ease. HPL? 6 euro for the 80w ones, even the comfort/deluxe ones. Fluorescents? A whole box for 25 euro or something. CFLs? Well, they've been gone from the stores here 10 years ago already because no one wanted them after LEDs were introduced. But at the thrift shops you can grab them for very low prices, though by now you're finding more and more LED bulbs in the bins with the bulbs, because of the natural end of the life span of the CFLs. But if you'd been there at the moment of the switchover, you'd have been able to get bins and bins of CFLs and assorted incandescents.
SOX is the only exception to this - those are expensive, and always have been, it seems. Though (i think Indian) new production SOX'es are available from www.dbl-verlichting.nl for a price that i think is fairly reasonable.

The ban affects only things that are/were in current production. All the older stuff will be as easy or hard to get as it is now. Just slowly getting harder to get, because that's how history works. Same goes fro antique radio parts, antique car parts, antique music instruments... It's not because of the bans of today, that the products that went out of production 40 years ago are getting harder to find.

in Canada the Minamata? agreement came into affect this year and i have seen MORE fluorescents for sale including a 2 pack of CFL 13 watt at the local grocery
Home depot has new circline tubes in stock

 I don't see that happening until long after we're all dead and buried .  There's still just too much of it around with some still in production . If all of the non-LED products were to cease production right at this very minute , there'd still be enough back stock to keep going for a good while . I very highly doubt that there'll come a day that they'll go scorched earth and shut down all of the non-LED plants and destroy all stock in the warehouses in one quick sweep! No company can afford to do that .  It will and IS happening but it won't happen over night . Besides , look at just how much 100+ yr old lighting is still available online as we speak .

Other good example is vacuum tubes. While some models are still producet there are plenty of old tubes left even from types that has not been made for decades.

If you're talking about availability retail, it's already happened here. 

 There's a lot here that you can't find in stores anymore that's still readily available in various locations online .

But if you want to see it before buying you're out of luck.!

Exactly !