Welcome back!
I think you can still find them, but not easily. I don't think a Queen Conch would be appropriate for any but the very largest tanks. Otherwise they starve. Fighting Conches are around two inches long, and make for great sand bed cleaners. I've had one for years in a 180 gallon tank. They are easy to find. Even these can starve in smaller tanks.
My favorite snails are reproducing Strombus and Cerith snails. Strombus are hard to find but Indo-Pacific Sea Farms sells them, along with a lot of other great clean up crew critters. ipsf.com