Don't know about any good rivers (I haven't be out there in a few years), but I know there's a few big burrowing species out there so watch for the chimneys. Are you going to be using traps, nets or trying by hand?
(and if you find any of these, sell me some! Since you've got a lot more species out there than I do here lol - Cambarellus puer, Cambarus diogenes, Cambarus laevis, Cambarus robustus, Cambarus rusticiformis, Cambarus tenebrosus, Fallicambarus fodiens, Orconectes lancifer, Orconectes luteus, Orconectes placidus, Orconectes stannardi, Procambarus gracilis, Procambarus viaeviridis)