I have croupers on my llama saddles. I don't like them and the llamas like them even less but they do work. Normally I leave them loose and laid over the back of the saddles until I'm going down something steep.
I'd like to replace them with britching but so far I haven't found any that will fit my saddles. I'm about ready to invent my own but they'll have to be nylon. I don't have any way of sewing leather.
Get a quality punch and a speedy stitcher. We've done that to repair leather. It's time consuming, but you can make it exactly as you want it, rather than adapting gear made for a different critter. Probably not a lot of commercial llama tack.
As Vince stated, you can rivet the stress points.
