Yes, I do. And flea markets, second hand stores, and Estate auctions. I don't do yard sales because they rarely match my free time, and pawn shops tend to have more modern "tactical" blades (which to me says something about folks who tend to carry such knives). Here's a picture of one weekends haul from a few months ago:
I paid between $1 and $15 for any of these, and that includes 2 Schrades, a Case, 3 Imperials, a Iriquois, a Utica, and a Kent, plus a couple others. Cleaning up knives like this has taught me a fair amount about quality and construction.
Here are some of the beeter finds from the past 6 months:
1st, a Remington UMC Jack -
This is a Fight'n Rooster Gunstock Whittler; German made and tight as a bank vault -
Here's a John Primble marked Schrade, still in the box, a very hard to find knife -
And here's an old Queen Stockman in their beautiful Winterbottom bone -
I've bought a fair number of knives just checking out places; it's part of the fun of going someplace new. Yes, there's a fair number of overpriced (and in some cases fairly priced) blades hanging around, but there are bargains if you look.
If you're interest is in knives from the lat 20 years, or "tactical" folders, or purely custom blades, then you're going to be limited in what you find. But if you go looking with an open mind you'll find some neat stuff.