(I will note the basset clarinet is almost always in A)
I've played bass in bands for a while-I've seen a few parts with a low C-most recently Omar Thomas's Of Our New Day Begun, which has some low Cs and a lot of low Ds on the first page! Generally most stuff won't have a low C unless it's from after about 1985 or so, roughly.
Benedict Eppelsheim makes a Bb contra, but I wouldn't call anything of his "normal production"
Buffet also makes contra-altos!