I ordered from T of W around 8 years ago, last order, and they shipped flintlock gun kits, unbreeched barrels, and locks with no problem.
I looked over their site just now and don't see any indication that they won't ship the same now.
T of W parts sets are just that. They are not kits in the sense that the parts are only available as a package.
Every part is available as a stand-alone product, and there is no discount for ordering the parts together as a set.
So, if you were concerned about ordering a kit from them and having it stopped at the border, you should still be able to just place separate orders for the parts that make up a kit. Say an unbreeched barrel and a lock and some other parts in one order, and the inletted stock and remaining parts in the next order.
When I ordered from them, their parts descriptions on the customs declarations were kind of amusing.
The unbreeched smoothbore barrel was described as an iron tube and the lock was described as a set of machined castings.
This is true enough as the barrel and lock were in the white, with no finish applied.
There are a few small outfits that import kits like a Lyman Great Plains Rifle into Canada on a small basis. Don't know who they are at this point though.