Congrats on getting your RPAL - you're in for some fun! IPSC is a lot of fun!
As far as having stuff in stock in Ottawa, Millbrook generally has a good inventory, they recently started carrying IMI who make some decent poly mag holders. I've found getting stuff is often easier by ordering online, as it usually comes down to when I want it nobody has stock locally. SFRC is not that far from you, they often have good stuff, and it's just a fun drive down 15.
Since you already have a holster, you're basically gonna need mag holders, some extra mags and possibly a 1 or 2 piece belt, oh and make sure you get an uplula loader too. For mag holders, it's either polymer (blade tech, IMI etc), soft (Tyr) or magnetic (Ghost, CR etc.). For a belt, the 2 piece ones are nice, an inner runs thru the pant belt loops, the outer piece has all your junk on it and velcros to the inner. A stiff 1 piece also works well, tho you have to put everything on and take it off every time you use it.
For mags, 6 is about the minimum for ipsc, tho I carry 10 to any match and practice. Even tho a stage may only have say 14 targets for 28 rounds, you may do 3 mag changes depending on the stage layout. One of the stages as the recent RA match had a couple of guys doing 4 mag changes.
If you're interested, we run an IPSC / Practial Shooting club at Stittsville, we practice Sundays all year round and Wednesdays April to Oct. We have a ton of fun with pistol and rifle (and the occasional shotgun). PM me if you want any more info.