That part that connects the rubber hose to the heater is nothing more than a homemade "L" .... Looking at the picture below you will see the 90 degree elbow which hooks to a piece of copper tubing that is sandwitched in between the two fittings. The hose I bought at Tractor supply and can be hooked to your heater without the "L" (the rubber hose end is the same fitting size that is at the end of my "L")....that part just happened to be on the heater when i purchased it used and i almost didn't use it as it wasn't needed.
The "factory version" of that is available from Camco Manufacturing, which sells the Wave heaters. To quote their description: 90 degree elbow, 3/8" SAE mail with 3/8" SAE female connector. Full 360 degree swivel." Part number is 57633. I'm using one at each end of my copper line; one at the heater and one where I'm teeing into the existing system. At the heater end, it makes it possible to convert the side exiting connector to one that aims straight back, or up, or whatever you choose, in very little space. Cost is 11.95 plus shipping, so they're a bit pricey, but they have advantages in close quarters. Phone number to order is 800 334 2004. www.uscatalytic.com
, but their website is not very good. You might search and find a better deal. They're not available at Lowes, but haven't checked elsewhere.