Dwarf crayfish are the only crays considered fish-safe. There are several places online that sell them, and I believe some AC members also do. Search the classifieds area here.
There are a few different species of dwarf crayfish, but all are in the genus Cambarellus. C. schufeldti, the Cajun dwarf cray, is two-toned light tan and brown; it comes in a striped and an unstriped morph. The Mexican species C. montezumae is similar. C. patzcuarensis, another Mexican dwarf cray, is bright orange. There are others, but I haven't seen them for sale.