"Bacillus thuringiensis - Kurstaki" is available many places, around here, as Thuricide, Dipel, or even at the local Best Buy hardware store under the stores brand name. I have not seen any at the big box stores around here but the locally owned nurseries here carry it and if you ask for BTK most clerks, not all, know what you want.

Bt-K will have no effect on sawfly larvae. Only the larvae (caterpillars) of moths or butterflies are harmed by feeding on the product. Sawflies are larvae of a type of wasp-like insect.