El Mar only carries OMS BP/Wing combos as far as I know, but they say they can get anything. El Mar is, by deliberate choice, non-tech, so you won't find many BP/Wing advocates there. A couple of the people there like Vic and David (the repair guy) have tech experience, and they both dive OMS, if I recall correctly.
I believe Ocean Planet carries Dive Rite gear, and I've been fairly happy with their prices (bought my Pressed Steels LP104's from them at an attractive price).
Scuba Sciences (Central/West Valley) carries Halcyon and Deep Outdoors (unless they dropped those brands in the last year. I haven't visited them for a while).
I don't know of any places where you can try the Koplin BP or the Oxycheq wing, but they look pretty similar to Halcyon (though I've heard that many people like them better).
I have both double and single Halcyon wings, so if you get really hard up on wings, send me a PM and I can meet you at El Mar (10 minutes from my office) for a go in the pool with them.