I've found several guns, mostly pistols but two shotguns, divided between Saskatchewan & Alberta. Spent MANY hours in the dark, in crappy weather, snow, wind etc. looking for them too.
I'm on a Search & Rescue team, and it's very common in many jourisdictions for the local SAR teams to be called out for evidence searches after the commission of a crime. Tends to be a good deal for the Police; SAR teams are all Volunteer, and every Province requires members to qualify to a specific standard before being allowed to participate in searches; one of the qualifications is a Police enhanced security check. End result is the Police get a lot of qualified, trustworthy & experienced people out for the cost of an urn of coffee or couple flats of bottled water, many more feet on the ground looking, and the people doing the looking usually have a lot more experience searching for things than the average street constable does.
I've never been involved in finding anything really exotic, but I know of a B.C. interior team finding a loaded & fully functional MAC-10 just off the side of a secondary highway. As I recall it was a road used regularly for smuggling narcotics across the border, & the weapon was connected to that "industry".