they're discontinued, you need to find old stock ones and they aren't as cheap as some other chips, that's for sure.

if you type AN28F512-120 into ebay you'll get plenty of choices.

as long as they say 'AN28F512-120' and have the big intel i on it, they should work fine. the long code at the bottom doesn't matter.

don't buy -150 chips, those are for 96+ ecms, they're a different speed