I had a difficult time looking up a double bit handle about 4 years back and lucked out finding a Lee Valley staffer who knew of some secret non-regular-inventory stash that the others didn't know about. Theirs was for the oxhead that they sell but I was able to whittle it down to suit my need for the vintage forge-welded Swedish head that I have.
You might find some luck with this outfit, I might even order a spare for myself.
https://beaver-tooth.com/collections...it-axe-handles