Ya, this is actually probably the biggest hurdle of cold water tanks: livestock. It is unfortunately (or possibly fortunately) illegal to collect sealife here in BC. You need a scientific license to do is legally (believe me, I've considered this on more than one occasion). And to make matters worse, there are no LFS around here that do any coldwater livestock that I know of. That being said, it can be done. You can collect on the sly (though you really shouldn't) and I know of some importers that can get some really sweet coldwater livestock (like Shaw's cowfish).
Our "deep water" species around here actually don't start that deep. Our waters get pretty dark pretty quick. When I say deep water I am meaning something that lives more than a few feet deep and isnt algae. When diving I come across tube anemones and painted anemones (I want a tank for one of these alone) as shallow as 10ft. All of the cool skulpins can be found a couple feet under the water and at night time you can find them right at the surface.
Probably your best bet is to try the tidepool approach for now. You can find brooding and strawberry anemones in tidepools and some times some green ones if you know where to look. Decorator crabs are a cinch to find and starfish you don't even have to try for. If you go some place like Ansel point, just past west van, at low tide you can access a rock wall that has a lot of these sorts of small to medium size tidepool and deeper water species within arms reach. Vancouver island will be even more successful.
I'll leave the logistics of this ip to you
Don't muck up my favorite dive spots though!
But really, I think a cold water tank would be well worth the effort needed to plan one out.