You can get inserts complete with allen key head bolts from bunnings. However, I use stainless bolts with countersunk heads (also from bunnings) right through the board for my homemade ply boards though..they will never pull out!
If you dont want to drill into your board you can get stick on threaded mounts made by NSI (North Shore industries USA). Call in at the kiteshop for info if you are interested or email me, another option is the stick on deck pads with threaded inserts ready for foot straps also made by NSI.
i have built a lot of kiteboards and have what you are looking for they are called threaded blind inserts i had these made for me so if you want some just email me there are cheap as i have alot of them
