Hard to find, or expensive, or both include:
spare tire carrier (available as a repro, or I may know of a "project" one for you)
gas tank (not hard to find, just hard to find a good one. Once a truck has the bed removed, the tanks don't seem to last long)
rubber floor mat (I used to have several, but recently sold my last one, except the one I'm keeping)
deep sump oil pan
original 235 engine (seems like most have been swapped out)
decent bed (if you have the fabrication resources available, there are drawings available)
rear shock absorber kits (hard to find)
windshield frame (available as NOS or repro, but expensive)
wood steering wheel (duh!)
etc., etc.
Ive had a number of ebay searches set up for several years, and I just keep an eye on the results. I've found nearly all of my bearings and races this way, and rarely had to pay much for any of them. For instance, there is and original master cylinder listed right now... I almost bought it, until I checked my parts shelf, and realized I already had a NOS one.