Such trim parts will be hard to come by new. Try junkyards with the one you have. You should know
The GMC Jimmy should have many parts in common with 1994 CHEV Blazer S10 or Oldsmobile Bravada. A Bravada could be an easy replacement because they sold many in red.
Also try looking for the full size Blazers and Tahoes.
The seatbelts in the rear are fixed with a TORX 45 or 50. The cheapest way is to buy just the socket for a wrench or a set of keys like Allen keys in a bundle.
With that you may be able to remove one of the bolts on the Plenum. (Not too sure what you intend with Plenum Cover - may depend on the engine type - VIN W or VIN Z - TPI vs. TBI).
Sourcing the bolts once you have the dimensions should be easy.