Turtleshack is not good (even though as I type this, there is an ad on this very page lol)!! They do indeed have a reputation of selling sick animals. I once purchased a Mississippi Map from them... it came in a shipping box. Thats all, just the cardboard. No insulation, no carrier within the box. Just the box, like it was a DVD or something. It survived the shipment but died of disease a week later.
There are a lot of good places to pick up turtles online. Check out turtleforum.com, there is a section of the forum that deals exclusively with finding reputable breeders. The above mentioned turtlesource.com is pretty good... I just acquired a nice florida snapping turtle from them about 6 months ago. Nice specimen.
As for tank mates, almost any slider or cooter will be ok as tankmates. Or you could always pick up another painted, there are several variations (western, eastern, midland, southern).