There are two ways that I know of.
One is to pay for one, and hire a professional one. That'll cost hundreds of dollars a day though, so that is probably not practical.
The other way is to get a free coach. Which you can find in the form of a fellow competitor, if you become involved in competitive shooting. You'll pay for your "free" coaching, by spending hours (years in fact) on a rifle range. Which is only a good idea if you enjoy this....!
There are a number of very good fullbore shooters in Quebec, but I don't think any fullbore is being shot in the Montreal area any more (the 1000 yard range just east of Mtl. has been closed to shooting for several years now). There is fullbore shooting done in Quebec City at Valcartier (a nice 600 yard range), if it is practical for you to shoot there you should contact the PQRA /ATPQ (P.Q. Rifle Association) and ask them.
There is also some very good fullbore shooting done in the Ottawa area at the Connaught ranges (a 900m national facility, where our annual championships are fired) by the NCRRA (Natl. Capital Region Rifle Association).
Visit either of those, and look into fullbore shooting (either with iron sights and sling, which is known as "Target Rifle", or with a scope and rest, which is "F-Class"). You can spend a lifetime mastering it, if you are so inclined.