I had a loop missing on my cover and it the others have a little plastic loop that the tiedown goes through on them. I took a shot in the dark and asked for plastic boat cover parts and got this site. They have a tone of this stuff and other little things you may be looking for. I found my part and it is called Loop Lock 1" Black and ordered 8 of them along with 10' of 1" 900# polypropylene strapping. It is more then I will need but may come in handy one day. Check them out and see if they have what you may be looking for in fasteners etc.

http://www.sailrite.com/