A coldwater tank is definitely on my list of future aquariums and I've done some research on what goes into them.
In California is pretty much completely illegal to collect any livestock without a permit that is super hard to get. There was one online retailer that was the main supplier of coldwater livestock to the aquarium hobby, but they just recently went out of business. They were based in Portland and mostly collected along the Oregon coast, which is a similar biotope to Norther California. Hopefully a new company will step in to fill that area now because I don't know of any other suppliers. Josh and Stu (the former owners of Coldwater Marine Aquatics) are both active on Facebook, so you could possibly reach out to them and see if they know where you can get coldwater livestock.
In terms of setting up the aquarium, you'll definitely need an acrylic tank for the insulation. The thicker is better with a minimum of 3/4" thick for a smaller tank. You'll definitely want an acrylic lid too, because you want it all insulated. Also, the sump (if you have one) will need to be thick acrylic with a lid to keep it insulated as well. Another sump suggestion is actually to use a hard side cooler with a lid. I believe you can run coldwater tanks with less filtration, since coldwater is generally much more nutrient rich. Also, since there aren't any hard corals or even as many photosynthetic corals in coldwater, you can get away with lower lighting than an SPS or mixed reef tropical system. The other big differences is that you normally use a courses substrate and different rocks to replicate what you would see in a natural coldwater environment. Since there are a lot of non photosynthetic anemones and corals in coldwater, you will definitely have to feed the tank. Oh, and of course you need a powerful chiller. You'll want to keep your water around 55 F for a Northern California biotope, I believe.