You should have no difficulty getting to the campsite: most GPS knows the campsite and you will find many signs along the road as you approach the campsite. The roads are wide and passable to the campsite, whatever your equipment.
Here is some information to make your journey easier.
The address of the campsite: 11 chemin de la Rodde, La Garandie, 63970 AYDAT
If you are arriving from Clermont-Ferrand, it is simpler and quicker to avoid the town and Lake Aydat by going via the Col de la Ventouse. In summer it's often crowded around the lake...
GPS coordinates of the campsite
Lat. : 45.6635686
Long. : 2.94762630
And if necessary remote guidance on 04 73 79 33 90
Good road !