You could buy system and data from MTH. Pretty sure it was almost offered to me once. I think all the PS-1 parts were up for sale or being considered for sale. Here is your problem. The chip that is used is obsolete. So even if you had the program and data what do you put the new data on? Same reason PS-2 5V and later 3V became obsolete. The old service manager was doing last buys of the chip. So what MTH has in stock is all there is.
So have you actually wrote to a chip one of your stored ROMs and produced your own new chip for use? Are you going to invest in some sort of adapter board to make some new type of memory work with 1980s tech?
I still do PS-1 repairs, but each year less. But still plenty of upgrades especially Premier Steam. While I am sure there are unique sounds like Gas Turbine and some other passenger effects. The diesel stuff was pretty generic and the freight even more so. There are tons of this stuff out there still. QSI was for sale too.
Lastly, I think I can count on one hand the times I had to replace a chip. And I have done hundreds of PS-1 repairs. Physically breaking the chip or a leg, and the extremely rare chip failure. All most all repairs are board or software related. And those tech chips from MTH don't resolve all those issue. My secrets from doing this. 
G
