Hiking straps are sewn to the trampoline, so technically, they're not a separate part.
If you want to replace the straps with something close to original, take the tramps to a canvas shop and have them sew on new webbing (you can order UV resistant, polyester webbing from most sailing supply houses [West Marine]). A nice trick they do on new tramps is to put a 1/2 twist in the webbing on each "bay" of the strap. Makes the strap stand up a bit so your foot slides in easier.
Or, you can get a grommet kit, put the grommets in yourself and run line / padding or webbing though them to make your own straps.