Welcome to BYC! Maybe @Wickedchicken6 know where to get grit.
Hello and welcome to BYC!! It’s so nice to have you join us.

I'm next door in Manitoba.
In regards to grit, I've been getting our grit from a local independent company. I believe Masterfeeds is their supplier for their chicken feeds so it may be that they get the grit etc from Masterfeeds as well. I know Masterfeeds carries an oyster shell/grit combo, so I would phone and ask your nearest Masterfeeds dealer about grit.
https://masterfeeds.com/
I don't see that TSC has grit. But if you have a store close to you I'd inquire about it.
https://www.tscstores.com/
I would also think a co op agro store "should" have grit as well. I buy my oyster shell from my local co op.
This is the brands I've purchased. Perhaps the name brand can help if you're asking businesses. If you have any further questions, please don't hesitate to ask myself or others on the Canadian thread. There may be members in Ontario who may be able to assist you better than I can.

https://www.backyardchickens.com/threads/canadians-check-in-here.144/


Cherry Stone grit. I had no idea it could be used in aquariums until I read the bottom of the bag when I took this picture...lol.

This Pacific Pearl Oyster shell is purchased from our local co op agro store.