Gravel has a contract with RemArms and that gives them the exclusive distribution rights for Remington spare parts in Canada.
So, if Gravel can't help you .... then you will have to look in the US.
This is an authorized Remington repair center in the US and they have stainless bolts in stock. However, their contract with RemArms does not allow them to ship to Canada.
So you will have to find a way to bring that spare part into Canada yourself.
https:// gunrepaircenter.com/
I bought an 870 stock from Gunrepaircenter.com at the beginning of the year .... and that Gravel told me they could not get. I had it shipped to a holding address just across the border, and then drove down there to pick it up and cross the border with it.