In case anyone still cares, I found a good variety of battery springs for our purposes in the form of these
RC remote springs. Note that there is both a positive spring (nearly flat, and with a crosspiece to touch the button) and a negative (much more raised). The
coils are about 6mm across (easy to fit into a tight space, could even get them inside some of the larger models of eCig), 22mm across for the pair, and 16mm between centers (so usable for pairs of
batteries from 14mm to 18mm), or cut them apart and trim as needed. 7 to a pack, $2.89 at this store (they're carried at a lot of RC shops).
They will meet my needs just about perfectly, your mileage may vary.
--Dave