If you are interested in the R-390, R-390A, R-392, etc... we have our own list going at;http://mailman.qth.net/mailman/listinfo/r-390
There are a few hundred members all over the world. A very large pool of talented individuals, many who have been working on the radios since their term of military service back in the 50's and 60's. It is a fairly active list with everything from those who are just interested up to the folks who are actively developing mods and techniques to continue to advance the art.
It is not all just about keeping to the gospel of the original designers, there are many new ideas, minor component value mod changes that are extensively tested before becoming generally accepted changes.
If you were looking for services to help with a restore, someone to guide you along on a restore of your own, the latest source of information or to bounce ideas off of friends in how to do something weird like compensating the PTO, antenna baluns, painting or clutch pack disassembly. Those people are there.
Yes, the radio is very intimidating looking when you see the gears, cams and inductive slugs all doing a strange dance as you tune the radio. We have good procedures in how to do rebuilds, people who have access to spare parts and even people you can meet locally to take a receiver out for a drive at their QTH. There are as many non-hams on the list (premium RX users, DX chasers, Utility/ BCB/ SW chasers) in addition to hams who use the receiver as part of their station.http://www.r-390a.net/Y2K-R3/index.htm
I work with premium receivers as well as the R-390A and the SP-600. There is a great deal of cross-pollination on the list from very smart people. Conversations can be as simple as how to remove old grease up to theoretical discussions on propagation theory.
Y'all are welcome. Join it for a while, introduce yourself and look through our archives.