Note - instead of buying the pulled dram, if you have access to a heat-gun, it might be much cheaper to buy the right 72-pin ram, and desolder the ram from there and solder it to these boards. Also, supplies of 72 pin ram isn't exactly scarce anyway :-)
There are probably (I guess?) a bunch of compatible RAM, I will try to make a list. For those with the will to trade on alibaba, this might be the correct dram;
https://www.alibaba.com/product-deta...838.0.0.ZvdQEE (alas who really know..)
Edit (1): I compiled a list of might-be-compatible 1Mx4bits RAM, however im not really that much of an expert, so if "someone" would revise the list :-)
Hitachi: HM514400
Samsung: KM44C1000
Mitsubishi: M5M44400
NEC: 424400
Toshiba: TC514400
TI: TMS44400
MicronTech: MT4C4001
Hyundai: HY514400
Edit (2): I went through all the datasheets of the above, and I came up with these model-numbers (and their speed). One has to really double check the datasheets before bying in bulk :-) I do not know what the overall maximum access time are for the RAM, however the one djbcoffee linked to is 60ns, 16ms refresh time, 300 mil SOJ.
Samsun KM44C1000DJ-5 (50ns)
Samsun KM44C1000DJ-6 (60ns)
Mitsubishi M5M44400CJ-5 (50ns)
Mitsubishi M5M44400CJ-6 (60ns)
NEC PD424400LA-60 (60ns)
Toshiba TC514400ASJ-60 (60ns)
TI TMS44400-60 DJ (60ns)
MicronTech MT4C4001JDJ-6 (60ns)
Hitachi HM514400ASLS-6 (60ns) // probably one of these triplets
Hitachi HM514400ALS-6 (60ns) // is actually right
Hitachi HM514400AS-6 (60ns) // so beware
Edit (3): Removed >60ns chips.