Lots of manufacters still make shocks for your truck. If you want to save research time go to an aftermarket site like Classic Performance parts or No Limit Engineering and read the write ups on the shocks they list for you years. A lot of times they have different characteristics than the old monroe stock shocks had. Some of the new ones damper out bumps and improve the handling like Doetsch Tech Nitrogen Gas Shocks. The bad side to these is that they are costly compared to basic shocks. It all depends on what you want to do and how much you want to spend.
Alternatively Ebay regularly list air shock setups for about 79.00 for the rear. I'm not sure on the ride characteristics or the quality though. Hope this helps.