for Strap repair in general
look for a saddle or harness shop. you can ask you local tack shop, they should know who repairs heavy webbing and leather near by ( some time a shoe repair shop can also do it) . Most upholstery shop will not have heavy enough machines to fix it to original or close ( there are some). they need to have what is called a 7 level machine or the ability to Sew 277 or thicker nylon thread we fix ours with a 325 thread. If I have any question we get rid of them. just my.02