Assuming that by
foremost shower faucets you meant "for most shower faucets", most parts need to repair shower faucets can be found at Home Depot, Lowe's, hardware store and plumbing supply houses. These parts are generally confined to the internal working parts of a valve. Some after market trim parts can be found.

No, they mean the brand 'Foremost', which unfortunately no longer makes this part. I have the same problem and spoke to the supplier who confirmed this for me. Home depot, Canadian tire and Rona all used to stock it but the part has long since sold out

This web page shows Home Depot carrying some Foremost products.

Foremost | Water Supply Lines with Escutcheon | Home Depot Canada (http://www.homedepot.ca/product/water-supply-lines-with-escutcheon/976748)