Hi Bob and welcome aboard. Sounds like you're well on your way to having your own sub! Great news to hear from another builder.
Many of the electrical parts used are from automobiles and golf carts.
If you are looking for 36 volt motors you might try a golf cart parts house, or look on-line at the folks supplying the home made electric car industry.
Large diesel truck junk yards may also be a source for electrical parts.
Many of us are using the Minnkota 101's because they are the simplest to adapt but they don't have the bulk power of larger motors used in golf carts. Lots of power is good but often times not needed, as most of the subs are operated at such slow speeds. Another nice thing about the Minnkotas is you can use the factory speed controllers. Very efficient, relatively inexpensive, and readily available if you need a replacement or just want a spare around.
For my sub I used 4 Minnkota motors but really expect to mostly use just two at 1/4 speed most of the time.
Mine were $239 ea. with a speed controller at $129 ea. and a prop at $36 ea.
Prices may have gone up a bit but they are the cheapest place and give good service.
Great to have you aboard and good luck with your new boat. Ask lots of questions and try to make next years convention in Florida. It's LOTS of fun.
Frank D.