I don't believe that there are any right now... but there will be a large selection in the future.
here are some companies that make exhausts for the E46 and other BMWs. I will put thumbs up for the most popular, not that they are better just more comonly used. For the E46 M3 they range in price from sub $1k to over $5k, with most being between $1k-$2k
Eisenmann
Supersprint
AC Schnitzer
AA Tuning
Borla
Dinan
UUC
Remus
Amuse
B&B Triflo
Cargraphic
Dixis
GruppeM/Motek
Kreis-sieg
Larini
Magnaflow
Milltek
Stebro
Tubi