Fantoms seem to be somewhat uncommon but you still see a disproportionate amount here in Western NY, primarily because they were sold locally before the major national rollout and the inventory was auctioned here when they went bankrupt. Thunders are far and away the most common, though I did pick up a nice Fury recently and have several more in the shed I forgot even buying.
I used to buy them or garbage pick them years ago, unclog them, clean them up and sell them to coworkers. They're easy to work on for the most part once you're familiar with them.
The Drytech probably is not as uncommon as you'd believe. They had loads of them at Service Merchandise when they closed, enough to wall off an empty section of the store (and equally large numbers at a few others I visited). The thing is you don't use a carpet cleaner every day, most people use them sporadically. There are probably many sitting in closets out there (I'm starting to see lots of 1980s carpet cleaners at the rift stores).
All the others probably aren't terribly rare either. All the local Targets, Walmarts, Kmarts and Best Buys had Wildcats, there were loads of all the new models at the auction, and old ones as far back as 11amp Destiny models (I bought one, I'm guessing they probably had a few floating around as warranty replacements that were never used).
I spent a lot of time in 1997 in NYC there used to be a liquidation chain there called Odd Job Trading or something, I remember them having tons of refurbished Fantom Lightnings. While the power head on them had its share of issues, the canister body is pretty durable, there are probably quite a few floating around being used for quick clean ups.
Most of them were built fairly sturdy, especially Thunders, so they're not like other 1990s vacs where you seldom see them turning up working used and in good shape. I think there is more a fascination with them because they're somewhat unusual.