Diamond Chair Cushion Fix?!  

replacement hooks
those pesky hooks can be found here.
http://www.mancha.demon.co.uk/spares.html

String attachments for diamond chair cover
Do those pesky hooks also come with instructions on how to attach to the string and the chair frame? Mine is also broken but even with the right hooks i have dont think that i will know how to put it together without instructions! Thanks

Easy.
The hooks are simply crimped onto the string -- you could do it with a pair of pliers. The "string" in the Bird chair cover pictured below is plastic, but the idea is the same.
The hooks attach to the chair wherever you like; try to pick attachment points that minimize the strain on the cover while still holding it in place.

Diamond chair covers
Thsnk you so very much for your help!