Where have you looked? Have you tried a salvage yard, engine rebuilder shop, and dealership? What about eBay, there are often folks parting out their Explorers.
I sell thousands of explorer parts on ebay....usually 95-01 right now.....ebay name is automotive_unlimited....I have a plenum from a 99 OHV...still installed if that'll work for you...my phone is 1-740-596-2077 name is Tom