To OP: Re your second question, you'll probably be fine using hi-cap mags at the local fields in the Greater Vancouver area (i.e. Panther in Surrey, Bigfoot in Mission, and Tsawwassen Paintball). Most of the fields and clubs don't have specific restrictions on using hi-cap mags for their regular game days - many people use them. Check the forums for the various clubs (Fraser Valley Airsoft Assoc., Op-For Airsoft, BCAC) before going out on a particular game day just to be sure. Most, however, DO frown upon someone loading up with a few thousand rounds' worth of hi-caps, using a regular assault rifle, and calling themself a "support" gunner. It irritates me too. Of note, some clubs have specific rules as to what qualifies as a "support" weapon, and lay out different ammo limits, engagement distances, and have even discussed different FPS limits (not sure if this will be implimented though).
The only time you'll have an issue is with the longer tactical or milsim-type games, where they have specific ammo restrictions, and sometimes don't allow hi-caps. Like most of the others above, I prefer mid- or low-caps for their realism and reliability (and no rattle), and prefer more realistic ammo loads, but if all you can find is a hi-cap, then that's what you'll need to work with.
Sorry - I don't have any advice or suggestions re any other mag options for you.