One suspects most will be illegal with overpowered / wrong rated motors , plus a stand alone throttle that works independantly.Gum tree. Shpock. Next door website etc you may find builders. Some sell bikes as well
Agreed. It may be a bit daunting when you don't know what to expect, but if you are used to regular bike maintenance it is very straightforward.It's not exactly difficult to do it yourself. Why pay someone else?