When you need a specific item, you have two choices: you can keep looking for an undiscovered "find" in the local paper, junk shop or yard sale. Or you can go to a broker or EBAY and find exactly what you need, but be prepared to pay for the convenience. I've bought Altec tube compressors and mic pre's for under $200 in the past year. But if I needed a specific model next week, I might have to pay $600 to $750 to a dealer. If you want the stuff cheap, you are not going to be able to shop at the vintage gear dealers. On the other hand, if you need it now and it has to work correctly the day it arrives, you may have no other choice.
Contrary to some opinions, there is still lots of cool stuff left out there, particularly once you get past the couple of "name brands" that have been thoroughly hunted down. But if you've got the cash, grab a copy of TapeOp or Mix magazine and check out the used gear dealers that advertsie in the back. Most have websites that list their stock.
Warning: the used studio gear business tends to operate on the "broker system." What that means is that the dealers often do not own the gear they are selling, rarely have they ever even seen the shit. Some guy with a studio in Kansas has an old Ampex he wants to unload. He calls a broker in California who has a big ad in Mix. That broker advertises the Ampex on his website. A hundred other brokers see that ad, copy the photo, post the same ad on their website, and suddenly that Ampex is being sold by hundreds of guys who have never even talked with the current owner. Thats not how many of us would prefer to purchase our gear. But its a quick way to find that unusual item you might be looking for.