I never found those either, after hard search.
Its easier to just use regular hooks , D-rings or replace the trailer mount with a D-ring on a swivel


EDIT:
Got these
Plastic Adjuster with bar Swivel Clip D-Ring Loop Insert Buckle Backpack Straps
( 253202584747 )QTY: 10pcs Webbing Size: 1"(25mm)33.9 x 27.9 x 5.2 for 25 mm webbing for $1.83 delivered in 12 days on ebay
Hole was a bit small and the Dremel fixed that faster than ordering the next size up, which would have been too big
The thin webbing on the Burley straps tangles and bunches, so making my own and adding cinches to bags is the way to go.
Also a lot less dear