Absolutely everything is available in the GTA, at comparable prices to the US. You might save a few bucks initially here and there, but wait until you get the wrong part, or the wrong sized helmet, need to have a shock revalved etc, etc. Wait for the costs to add up sending the stuff back to the US.
SportscarBoutique, CSC Racing and Northern Performance will have all you need, or can get it. PLUS, if anything goes wrong, or you need service, you have someone to look after it locally.