Hi Ed. Hamilton here. A great local forum for the GTA is http://www.gtaaquaria.com/forum/index.php
A lot of us hang out on there, you'll find a B/S section like here with plants, fish, tanks, etc. Us shrimpers usually have meeting now and again to trade/buy/sell shrimp, plants, etc.
There is also a great planted tank store in Markham called http://www.aquainspiration.com/
They have lots of stuff.
There is also lots of auctions in the area throughout the year, the Hamilton/waterdown one being a fairly big one with tonnes of things on sale for the auction.