If it comes in one of their kits biketronics would sell them separately and like was previously said I believe J&M will also.
FWIW, I don't like buying stuff from the stealer if I don't have to, but I have gotten some connectors etc from them before and they weren't too bad. May be worth checking out the instructions for some of the boom stuff - if they list a part # for harnesses etc. they are available. It may cost more than buying everything online at an electronics supply store for and making it yourself (I've done that before too), but the dealer stuff will fit perfectly and will look very clean - that being considered their cost is reasonable on some items. If you don't have a decent set of crimpers etc. some of the deutsch and molex connectors can be a pain when you have 4-6 pins in them and your crimps aren't high quality.
Freedom isn't free, remember to thank a vet.
2018 CVO RG lava orange, 117 Stage 3, 14" F47 and a few chrome extras. Boom crap gone.
2016 RG Special Cosmic Blue, 120ST with Dragos 2:1 and TTS tuner, FBI drop seat kit and JNR air ride. Stock audio long gone.