A Purasan is a Type I MSD, not a Type II. It is only legal on boats up to and including 65 feet LOA. Boats over 65 feet long require a Type II system, such as the Raritan ManaGerm, the aHead Type II system, "The MSD" type II system, etc.
Defender Industries out of Connecticut, or BoatFix.com, from New Hampshire, are among the least-expensive places to buy the equipment. However, I don't know that either one of them carry Type II systems.