The cemetery records for Hiram and Elizabeth can be found over on findagrave.com. And Hiram shows up in the Itawamba County, MS census from 1840 on. If you need any further help, just let me know. Best of luck in your search!
I took a look in the books I have and didn't come up with any matches for the information you provided. Just a quick question for you, was your ancestor John Richardson born in Itawamba County, MS to a Hiram Richardson? I found a John and Hiram that matched in that county; however, the mother is listed as an Elizabeth (Betsy) instead of the Nancy that you gave me with the information you provided. If this family is possible yours, I did locate the cemetery records for Hiram and Elizabeth in Prentiss County, MS.