As I said, I assume there are. The forums I read who used elements out of water heaters said things like DIY being cheaper. Can't be a huge market for 35 gal pond heaters.
Well the patio pond kits are coming out in all the stores. they are really neat. Lowes carries a really great one. It even has windows half way down the sidewalls that so you can view the fish underwater. The big pond I use to have I finally gave the fish away and filled it in because I could not keep the snakes out of it. I had a PILE of them...with a patio pond, no snakes and its easy to cover with netting. What is DIY? Lost me on that one. lol