I don't believe there is anyone in Canada breeding either of the species you have mentioned. I have seen a few Black Throats (farmed babies) for sale from time to time, but not as many White Throats.
I assume you are aware of the incedible size both these monitors attain, and the commitments involved in owning them.
Best of luck in your search,
JonK
PS - There should be a nice selection of Monitors at this show, and even more at the november show