Maybe McElhiney's? Also check the Outdoor Message for at least one other shop (don't remember who) that has an ad saying they specialize in target pistols.
The prices for anything from Europe are through the roof these days, though, and Earl's might be as good as any. They're great guns, but... that great? (They were pushing towards $2k last I looked.) Earl does sell used stuff as well, though.
Every once in a while a GSP turns up used on NES. I think the going price here for decent used guns is $1k or so, but with a lot of variance.