Why can't a vendor ship a firearm part from US to Canada

[rabe-5769]

I wanted to buy a sight for my rifle from a U.S. vendor but the vendor says that EBAY will not allow him to ship to Canada. The sight is not on the ITAR list of prohibited items. 

[marnotom!]

It may be because a lot of international carriers won't touch them with a ten foot pole.

MyUS is a popular package forwarder, and their list of prohibited items includes rifle scopes:

https://www.myus.com/benefits/shipping/customs-help/restrictions/

[rabe-5769]

Any type of optics ie: scopes yes iron sights no. USPS does not prohibit and handles them all the time.