They are standard 27 series CMOS EPROMs, MBM is what Fujitsu prefixed their EPROMs with and HN482764G would be a Hitachi chip.
If you really want you can ensure you get the exact same chip but any 27cXXX would work
so MBM2732A-30 - can be replaced with a standard 27c32 eprom
and NH482764G - can be replaced with a standard 27c64 eprom
The only slight caveat is the speed of the chip - the -30 means its a 300nanosec access time chip. As long as the replacement chip is the same speed or faster (ie it can be driven faster so the actual speed (set by the board) will be within its tolerances) you won't have a problem. Note that the lower the number, the faster the chip, ie a -10 is a 100nsec chip which can be read 3 times faster than a -30 chip. At the end of the day the actual speed may be less critical, its only if the board is really driving the chips that hard, I have never had an issue with putting any old eprom in without worrying about the speed, RAMs are a different matter tho.
I get all mine from ebay, a seller called IC-CHINA, sells eproms in batches of 2 or ten, great service, all eproms are wiped, programmed, tested and wiped again, they are usually very clean too, no gunk on the chip window from old stickers.
PS he has often sent me 12 when I ordered 10 to fill the chip tubes to stop them rattling about, happy with that!
