I'm surprised no one mentioned Steve Martin from Sidemounting.com. He also does a lot of YouTube videos and has an extensive amount of online training through a subscription that is well worth the price. Most of the training is based on X-Deep or the Razor. I've personally dove with him in the past and he is very knowledgeable and an excellent instructor.
I started out diving in the PNW and lived along Hood Canal just down the road from Sund Rock. Once I moved to Florida in cave country, I met one of Steve Martin's close friends named Joe Seda who also specializes in the X-Deep and teaches Steve Martin's system as well. Joe is who I took my sidemount class with, he is very detailed oriented about the system and goes over everything inside and out. We tested the system with everything from wetsuit to drysuit and aluminum cylindars compared to steel and what changes to the system should be made. He is located in the Gainesville, FL area and would be an excellent instructor. Looking back at diving the PNW, I would definitely go outside that area to get training. X-Deep is mostly used in the caves, so Florida cave country would be the best place to get your training. They can put you on the right track from the get go.
I would not suggest Dive Rite for sidemount compated to the X-Deep. I know some people who love Dive Rite and have no problem with it but I prefer X-Deep substantially more.
I'll usually use a set of LP85's with opposing valves although I really liked the aluminum 80's.
Hopefully this helps a little.