Those old Russian rangefinders are really easy to work on, so I wouldn't worry too much about finding someone who specializes in them. Any repairman who's seen the inside of a Leica ought not have a problem with one. So I'd search for someone local, so you don't have to mess with shipping and the hassle of email/phone communications. Plus there's less chance of something going wrong that is out of your control that way (like getting lost or damaged in shipping, or miscommunication with the repairperson). Though with the price these things go for, you might be better off just buying a replacement rather than having it worked on. You could probably by 2-4 of them for the price of a general CLA, and then just use the best one of the bunch. And if one ever breaks, you've got plenty of parts and a backup or two to get you by.