not too many years ago and fortunately for me, there were awesome deals to be found on craigslist daily, weekly at a minimum. And I mean unbelievable deals. But I just caught the tail end and in a matter of a few months everyone and their brother realized there was gold in them thar'; craigslist "vintage" audio ads and it didn't take too long before it turned basically into what it is today. Worked out well for me as I got to try out a ton of gear I never would have had a chance to otherwise. I would try it out and if it didn't fit into my plans, sell it and move on. Ended up building, what is for me anyway, a pretty decent system for not a whole lot of money (well, a few systems actually, tho I did learn I was not a "collector" and ended up selling my garage full of stuff and putting it towards one nicer main system)
BUT, tho not as easily found, I have no doubt the deals are still out there. You see people finding stuff all the time and posting on here. Wasn't tube stuff, but didn't someone just get a complete Spec system for basically nothing ?
I really have no interest in things which do not advance my main system anymore and as I am pretty pleased with it, I rarely even look anywhere. Even when the stuff was abundant, it did take a whole lot of time to find and get the stuff - often driving 3-4 hours one way then having to restore/repair it.
Takes work, but if you really, really want to find a decent deal, it is out there somewhere.
I now just leave things to the universe. Sort of put it out there and if it was meant to be, I will get it, otherwise I must not have needed it anyway.
If you really want to find something, will have to put in the hours going to every yard sale, flea market etc you can find. Question then becomes is it worth your time to do that ?
For me, as my main system got better, I had less and less desire and as the hours spent looking went down, the gear I found obviously went down.
Yes, in a way i was a fluipper as I bought a ton of things knowing I could sell them on ebay for a nice profit and I used all of that money to buy something better. But trust me, was not easy work at all. It really did take an enormous amount of time finding it and then going to get it.
Sure people stumble on things all of the time. I did quite a few times. But if you really want a "score", for the most part you have to put in the hours.
I was (am) retired so could look all day long. Now, could not tell u the last time I even looked at craigslist for anything audio or stopped anywhere to look for something.
best bet would be some of the following
let friends and anyone possible know you do vintage audio for a hobby and would like to find an "old" tube amp.
smaller estate sales that really are not advertised. many people do audio now for a living and if it is in the paper there is a good chance there will be a dozen guys there to bid on it or check it out. Look for the smaller ones where they really do not list everything , maybe not even the audio stuff. That is where you may find that old marantz tube amp for $100.00
Did I say ask friends
basically just how hard you want to work to get that "lucky" score. I had my share of lucky ones, but most had nothing to do with luck
With sharks circling behind me offering to double the seller's money, I got my wallet out as fast as I could, and made a mad dash to my car while dodging offers from onlookers. I spent the rest of the swap meet with a wide grin on my face, wondering how it'd happened. 
