I am not sure what he has but I know Alex71 sells bolts I dont know about complete kits but ide talk to him.
Also if he doesnt, look into something like this.
http://www.northerntool.com/shop/tools/product_200324972_200324972
Also, its never bad to have a small assortmant of cotter pins, o rings, hose clamps, an grease fittings. The sizes all depend on what you work with. Also are your quads an cars all metric or sae or both. Over the years we have bins of mixed bolts that are left over or from machines we got rid of. If a attachment is totally shot we take the bolts out and scrap it or rebuild it. When we were taking a section of a barn down we were able to salvage about 150 eight inch lag bolts. When I stop by the farm store I always check the clearence area for extra nuts, bolts, washters, hose clamps etc. If its 50% off or so and something i see myself using ile get it an keep it for when its needed.