Wondering if my 250w PSMH ballast can run anything else, specifically any HPS. The bulbs are kind of hard to find.

maybe a 400W MV (a bit underdriven), but with the ignitor disabled.
HPS do not seem to be that far away from the nominal spec perspective, but HPS are very sensitive specie, not only to the exact current, but mainly on how the current changes with temperature. You may try it, it will either run underpowered (check the lamp arc voltage at that state - if signifivcantly below to what the MH uses to work at, it may damage the ballast), or cycle if overpowered. Check also the lamp power (measure the V, A, the power is then approximately 0.9*V*A), if it isn't above the rated 250W, as that would wear the HPS quicker.
 

Notwithstanding Medved's reply, I would always urge caution. By and large, it's always preferable to run a lamp on the ballast it was designed for, and the same holds true the other way around. A 250W MH ballast was designed to run a 250W MH lamp, it's that simple, for the most part. Here in the UK, HPS and MH lamps are usually (but not always) electrically similar, so will run on the same ballasts, but that doesn't hold true in the US, as I understand it.

By all means experiment, that's how you find things out, but take care.

Here's a lamp for $10 O.B.O. + shipping  :  https://www.ebay.com/itm/166480430347   THere's also plenty of others for decent prices on eBay .

The best and most versatile lamp for this ballast would be a Philips Allstart CDM205/U/O/4K/EA...best performance too.

I'd personally get the CDM205 BT25 mentioned or any other 250w CMH lamp that would run on that ballast.

The CDM205s seem a bit harder to find compared to the rest of the range in the AllStart line.

I know the NYC OVZ use an electronic ballest for MH bulbs but are deployed with 150 watt HPS 100VOLT / euro bulbs so like mentioned above in Europe HPS and MV are sometimes interchangeable

 The NYC ballasts are made by Hatch and are M-102 spec which also runs a 150w S-56 HPS lamp .  Hatch says on the label "DO NOT USE Sylvania PowerBall lamps" . Why they specifically say no Powerballs , I have no idea .
 https://www.lighting-gallery.net/gallery/displayimage.php?album=5203&pos=45&pid=178180

Apparently there were two different revisions of that Hatch 150w ballast. Mine listed 150w M-102 and 150w S56 but also said not for use with Powerball lamps OR 942 series lamp. Not sure why.

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-199394

Somebody should try it and see what happens

 I wonder if someone like James or Max would know ?

Wondering if my 250w PSMH ballast can run anything else, specifically any HPS. The bulbs are kind of hard to find.

To answer this question, if the pulse start metal halide ballast in question is a 250W M138/M153 pulse start metal halide ballast, it should be able to run 250W H37 mercury vapor lamps decently well with the ignitor disconnected to avoid starting probe and resistor destruction because 250W H37 mercury vapor lamps and 250W M138/M153 pulse start metal halide lamps have the same operating current (2.15A) and the same arc voltage drop (135V). In some cases, a 250W M138/M153 pulse start metal halide ballast might be able to run 250W M58 probe start metal halide lamps as well if the OCV is high enough and that the ignitor is also disconnected. On the other hand, if the pulse start metal halide ballast is the less common 250W M80 pulse start metal halide ballast, which is often designed to operate double ended 250W “HQI” pulse start metal halide lamps, it will overdrive 250W M138/M153 pulse start metal halide lamps and the other lamps I mentioned above because 250W M80 pulse start metal halide lamps have a much higher operating current of 3.0A and a lower arc voltage drop of about 100V. Coincidentally, 250W S50 high pressure sodium lamps have the same arc voltage drop and operating current as 250W M80 pulse start metal halide lamps, which means that 250W S50 high pressure sodium lamps will run very well on 250W M80 pulse start metal halide ballasts without issues. Conversely, the 250W M138/M153 pulse start metal halide ballasts will underdrive 250W S50 high pressure sodium lamps and 250W M80 pulse start metal halide lamps.

Although I shared details on lamp specifications and interchangeability, it is still a good idea to run the correct lamps on the correct ballasts as others have said if you really don’t know what you are doing, but feel free to experiment as long as you understand the risks involved.

In your situation, is the 250W pulse start metal halide ballast have the ANSI code M138/M153 or M80? If you answer this question, you can look at the advice that I mentioned earlier in what lamps to use on your ballast other than the correct lamp.

It's the M138/M153 ballast. I guess I'll be sticking with MH then.

As I stated above, 250W H37 mercury vapor should run okay if you disconnect the ignitor as those lamps run at the same arc voltage drop and operating current as 250W H37 mercury vapor lamps.