@immatthewj, mostly eBay, also Brent Jessee. I look for 12ax7s and 6l6cg most
y vintage. However, I just bought almost new 3, 12ax7eh electroharmonix for $40, just because they seemed like a great deal. I’m always watching prices and really haven’t seen too many price increases or reduction in inventory. Maybe on new stock Chinese or Russian, but the inventory of vintage RCA black plates, telefunken ( just bought 4 red tips for $300) amperex ( bought 2 medical for $300) and what I’m interested in seems ok. Hope this helps.