You'll need item #4...both RH and LH brackets (only one shown on the diagram). These have the 2x2 cutout for the hitch bar. Any junked H3 should have em, as tow package models out-number base models about 10 to 1. There's a bunch of H3 wrecks on eBay. Even though your part may not be listed in an actual ad...they usually have an entire H3 they are parting out. Simply email the seller and tell him what you need. I've done business with Wayne's (in OH), Veldmans (IN), and Schramm (nationwide), and I've had very good results. A quick search brought up these eBay names:
veldmansauto
laceyautoparts
allwestparts
factoryoemparts2
BTW...there are lots of axles on ebay...both 4.10 and 4.56 versions. Its far cheaper to upgrade to lockers by swapping the whole thing...rather than disassembling your base-model single-track axles. You could probably score a AdvPak T-case too.
p.s. I wouldn't pay more than $50/pair for those brackets.