Memory hasn't been as finicky in years than I found it 10-20 years or more now, most seem fairly tolerant as long as you match up specs.
If using windoze, install cpu-z and just match the specs, speed, unbuffered, ddr-class, etc. Likewise using dmidecode under linux, just match spec what is there now. If using a mac, just pay whatever overpriced ram apple wants to sell you because you or your sponsor can obviously afford it. Probably a better way under mac, I'm sure google knows most sticks are probably compatible there too realistically.
I do miss when there used to be the technology swap meets over in Mesa here to find old/dated hardware for stuff like this, I think that all moved to Craigslist, now Letgo and others, always ebay if nothing else. I always buy used ram, particularly when talking the more pricey large ECC server stuff, really haven't had complaints personally doing so. Last time I put 128gb in my desktop, I did so for around a grand from ebay getting old server dimms from a retired cisco ucs box, same memory, which from dell would have been some $8k of absurdity.
-mb