Have you tried to contact some local shops? Many have a stash of spare parts they'll hook you up with for free or at minimal cost.
i live in southern california and in my area.. near the beach.. there aren't many snowboarding shops. actually there's just one mom and pop store within 15-20 mintues of me that thought they could help me find a replacement. i spoke to them and they didn't have the exact one.. and still wanted $15 for one used strap.. pretty disappointing. for that much i'd rather pick up a complete working used set of bindings or put the $ towards a brand new set.