There's a ton of 7", 7.5ips tapes out there in every idiom, but the ones audiophiles were more likely to buy were the ones recorded at 7.5ips. In the case of Popular Music, sometimes at more than one speed.
Everybody I knew back in the day stayed away from 3.75ips, but recording at 7.5ips was not a cheap way to do things, so you had to either transfer your off the air tapes to another format (Cassette, for some)
or be willing to part with $$$ and dedicate shelf space to tapes.
By the time I could afford my own machine, the pre-recorded boom was thinning a bit. I found the vast majority of my tapes in thrifts before that became "a thing". Same thing with my collectible (Shaded Dog and Merc) LP's.
By that time, I could afford the subscription to TAS, but not a whole lot of what I read about, so I scrounged before the auction site exploded the hobby into what it is now.
But there are yard sales every weekend. Grab 'em and growl!