I know that in the seventies lots of T. sirtalis parietalis were imported from Canada. Dutch reptileshops had thousands of them and they all looked the same.
They were every year available a few weeks after the snakes in Manitoba came out of brumation.
I a sure they were caught overthere.
The number of males was much larger than that of the females.
My first two gartersnakes were from such an import.

Great pics by the way!

I sure hope to go there one time. Manitoba in spring, I mean.