Ok, then I would suggest you try with Duy at AirsoftParts:
http://www.airsoftparts.ca/store2/in...ord=kwa+rubber
The EVO rubber is pretty damn good, if you want another one, contact him directly using the form on his website, he can usually get pretty much anything you need, and you will not find better service in Canada.
As far as I know 75? is fine for KWA/KSC guns, they use a ball bearing for a nub, so you want a harder rubber for durability.