Firstly, Rowly. I did not say SMB would not survive with LMB. I think I said that SMB would not reliably reproduce when combined with LMB esp in smaller ponds. The larger the body of water the better the chance of SMB successfully reproducing w/ LMB present. Both will co-exist, but the LMB will outreproduce and eventually (numerous yrs) crowd out the SMB if SMB are not restocked.
Secondly. If the snails are Physa or Physella yellow perch will clean them up. Species of snails in this genus have thin shells and it is easy for perch to crush them. Other snails such as Planorbids, Pleurocerids, and Hydrobids perch cannot eat.
Thirdly, Steve. Try contacting Dan Laggis, Gobles, MI (Laggis Fish Farm 269-624-6215 evenings). He does not sell pure bgill but may know where you can get some locally. Ridgeview Fin Farm abt 4hrs southeast in NW Ohio has pure bgill. Laggis is 3.5 hr from me been there couple times.