I am replaceing the foot rest and it has 3 rivets
that atatch it to the running board.

skidoo dealer does not have a part number for these
rivets and also told me that they are a spechial
rivet that requires special tools to in stall

I would like to make the sled look stock so any help would
be apreichiated.

When your sled was assembled at the factory they used a rivet called a "self piercing" rivet. You cannot duplicate this rivet except at the factory. The 'Doo replacement is a 390402200, which is basically an overpriced pop rivet.

Just go down to your local hardware store and buy a small package of stainless steel 3/16" pop rivets with 1/4"-3/8" grab. That's it.