How close to Calgary do you want? Need a actual campground or do you want 'crown land' where it's generally free if you're a certain distance off the main road.
A recommendation would be to find a close LRT Station (the trains that run around Calgary) and then park the Unimog there if you're going in to the Stampede. Parking is expensive and usually a **** show. LRT is much cheaper and usually faster. This is a HUGE geographical city and it's only getting bigger.
Let me know where you'll be approaching from (South, North etc) and I'll do some asking around.