Go to http://www.rvdealership.com/rvdstore/
In the Category drop down box select Water Heaters.
In the search box enter 3475.
White-Rodgers coil will pop up.
Order it, install it and enjoy your hot water.
Try digging around at PPL Motorhome parts site. RV Parts and Accessories for Sale - PPL Motor Homes
They had the single solenoid for around $30 but that was several years ago. It is a White-Rodgers part and it seems as though it was listed under the Atwood water heaters. Same solenoid. I may have the information at the MH but going to be several days till I can look for it.
I don't have time right now to research but I also posted this on rv.net too maybe five years ago. Might do a search there and see if you can find it.