Yeah I tried to buy one on craigslist but the guy was selling the whole pool, you take down and move. I offered to buy the filter, even to rent it, he wasn't having it.You're doing it all just right, just keep maintaining SLAM FC.
I guess if you happen to have an old cartridge filter lying around that you could add that to the pool for extra filtering. Dunno if you had a smaller pool before or not (the only reason really that anyone has those lying around).