I have located a local source of Thorite! I just spent the last 2 hours on the phone talking to all sorts of people who think I'm nuts for wanting a concrete product to use in an aquarium (yeah, tell me something I don't know!

) but I FINALLY found a stash here in town!
Some background though. "Thorite" as a brand name no longer exists (which explains part of the difficulty of tracking it down). BASF, the manufacturer, has merged product lines and the new product name is "EMACO R400 Architectural". There is another product people have been using, mentioned over at reefcentral, and that is "EMACO GP" ("general purpose"). Either should be fine to use. From what I understand, the difference between R400 and GP is colour - architectural is blended at a lighter colour to better match the colour of precast concrete products, since this product's "intended purpose" is as a patching mortar (concrete repair).
There are two local suppliers in Calgary,
1) Unicon Concrete Structures
and
2) Brock White (formerly Manstar)
I just spoke to the folks at Brock White, they have in their warehouse some 46 bags of the R400. It is technically "past shelf life" which means it is not warranted for structural use anymore but it should be just fine for holding pieces of liverock together. Because of this though they have a sale price on the bags at $31.86.
Here is the contact info:
Brock White
2703 61st Av SE
(403)287-5889
They close up shop at 4:30pm so go on a lunch break or something ..