I did some searching on the web with vendors Ive dealt with and didn't see any either. But that being said Im not the best at doing searches.
I looked in the board vendor list here:
https://67-72chevytrucks.com/vboard/showgroups.php
These are vendors that may have what you are looking for. A lot of the vendors on the list sell more specific items like suspension mods and such.
Try shooting these folks an email, even if they dont have maybe they can send you in the right direction.
Classic Bowties
Classic Heartbeat
Pickmup
Quality Classic Parts
GMC Paul