I used to get lots of vintage razors on Ebay. It was easy to find pristine examples for $5 or so plus shipping. Prices have gone crazy. Yard sales are the only place where I can find great deals now. I have a favorite user DE, SE and injector and a backup so I don't purchase many razors anymore. Vintage blades can still be found at yard sales.
eBay, etsy, garage sales, estate sales, auctions, flea markets, gun shows, coin shows, thrift stores, second hand stores, want ads, antique stores, barber shops, car shows, anyone I meet and talk to for more than five minutes, friends, neighbors, coworkers, hunting buddies, Craig's list, local second hand sale papers like thrifty nickle, trade days, the worlds largest yard sale, scrap dealers, metal recycling businesses,
I have been doing good at local Antique stores, there usually is room to barter. Some of the stores will look up the value before they price it, some don't. Yesterday I got a George Wostenholm IXL Celeberated straight in great condition for $14