I made some from a couple of old leather belts. It attaches as dan has described.
Walmart might have some First Act stuff.
Target might have some First Act stuff.
It's just a guitar strap. If you have one or get one with out a string ..... a pair of new "dress shoe" shoe laces in black, brown, or whatever color you want work well.
Or use a small rope, dog chain ..... whatever you can imagine.
I use duct tape or webbing for a lawn chair.
this site has some good leads on homemade straps.
these are perfect for CBG's...
How about modified dog leashes, or the same nylon 1" stuff from bulk rolls? Could use or discard the clip, cut button holes, any number of ways. It could range from a simple strap with button holes on each end, or simply screwed to the CBG, to a clip on both ends and an adjustable loop on one end. I have seen rolls at big box stores, military surplus etc.
I spoke to a crafter who makes various things from the nylon straps, including dog leashes and collars and such about coming here and posting an offer to sell some guitar straps. But I guess she didnt share my enthusiasm for the idea.......... I also mentioned crochet straps to my wife. She was not amused.