I have noticed lately, especially that the 3 way mogul bulbs are not as easy to find as they once were. Lowes used to sell the Sylvania brand and then GE but a year or two ago, they stopped selling them and they ended up at Habitat. (Since sold out, so I guess somebody has a use for them). I do still see them available at Ace Hardware stores, but the big box stores have stopped selling them it seems for the most part.

Not only that, but even medium base 3 way is getting less common too. Lowes has them but I did not see them at Home Depot or Walmart anymore.

It's not getting to where though 3 way lamps are sold yet the bulbs for them are getting difficult to find in the same store.
LED versions are available I guess but also not easy to find, and in many cases the bulb would cost more than the lamp.

I haven't seen the mogul three way incandescent bulbs in stores for around a couple years here. The medium three ways I still see in incadescent and LED. I think some grocery stores still stock them in incandescent too.

I suppose smaller hardware stores and lighting specialist retailers would still have the mogul three way bulbs though. It's a shame there's no drop in option for mogul three way aside from the original 100-200-300w lamp too, you can even use a medium adapter without losing the three way option.

Try looking for them on eBay. 

 Small hardware stores are definitely a good option for the mogul based 3-ways. I just got mine a couple of months ago from my local Do-It Best store for $5.99 . As far as I know, there's no option for a 3-way mogul to medium adapter without losing the 3-way option .

I haven't seen the mogul three way incandescent bulbs in stores for around a couple years here. The medium three ways I still see in incadescent and LED. I think some grocery stores still stock them in incandescent too.

I suppose smaller hardware stores and lighting specialist retailers would still have the mogul three way bulbs though. It's a shame there's no drop in option for mogul three way aside from the original 100-200-300w lamp too, you can even use a medium adapter without losing the three way option.

I have seen some mogul based bulbs with the 50/100/150W instead, but they seem much less common. Most I have seen are the Satco brand, but I have seen some vintage GE bulbs with that wattage combination.

Yeah I have seen the 3 ways in grocery stores, I haven't looked in a while though for them there.

I looked closer this weekend, and Home Depot does have 3 way medium base bulbs, the Ecosmart brand.

I saw some as well at Dollar Tree, but they were some no name brand, if I remember right. Also interestingly, they even had one Sylvania 300W clear bulb, which was surprising. And some Sylvania clear incandescent globes.