Welcome to the site from California. Nice to have you here.
As far as finding a hard bed liner for an 84, it will have to be aftermarket I bet, and I just have not seen one. E-mail the store here on this site (use the store button on top next to the home button), and Capt. or someone will let you know if they have any connections to those.
If you are talking about a newer bed that the liner will fit into your 84, again I am pretty sure that is a no. There are threads on here that discuss members who have done spray in bed liners and their results.