it's my first post here. I hope in proper forum section. :)
Last time I have made button icons for few PS2 and PS3 scene projects. I think they can fit also for PSX. They are all 24 and 8bit but should be easy to colour reduction and semi-transparent cuts (I have no longer use Optpix Image Studio and also I don't have Photoshop Sony plugins, so You are on Your own way to adjust gfx to PSX need).
I hope You will enjoy.