You have no TSC close either? That's a shame, its already hard enough for backyard chicken keepers to get necessary supplies in this province. You should start making a list of supplies to stock up on for next time. If you call the nearest TSC, you can ask them to order in grit for you for when your parents are willingtomake the trip,  but they're webpage is horribly out dated and it's very, very common for them not to have an item on their site that they definitely sell in store! 
I had to pick up grit in a panic a few years back, I can't remember the brand, or even know if the store chain still exists, but I was able to find grit for large exotic birds in a pet shop. 
We've got a cold snap coming, supposed to be down to -30c in some areas (including mine) tonight. I hope your crop problem clears up soon, we've been lucky this winter so far, but on these really crispy cold nights I like to toss outa bit of cracked corn make sure my girls crops are good and full so they can keep their little internal furnaces running on high all night. Chickens put out a LOT of body heat. 
Let me give you a bit of comfort though, I'm in Ontario too, and I've never had a chicken die because it was too cold in the unheated coop. Good luck!