I bought them from my local store so i'm afraid you'll have to go see any SD dealer and just order the pickup rings
FYI, i also got by using 6 string pickup rings, but had to carve them out a bit for the pickup to fit, though it laid nicely over the cavity of the active pickup. make sure you get long screws though as the holes for the pickup rings line up with the corners of the cavity so it's a long way down!