I agree! I lost two the other day. I think someone had some aftermarket ones that was a large quantity for like $12 or something but I can't find the thread about it anymore.
Seriously, if the aftermarket guys want to make something useful, some sort of twist lock permanently attached fasteners should be fairly easy and a good seller.
Search for the part number on eBay. I found them there for $1 each with free shipping. By far the cheapest way to get them. Same goes for the cowl fasteners.
Key to not losing those battery cover fasteners is to remove them entirely before removing the cover. If you just pop them up and leave them in the cover while removing the cover then they're probably going to fly off and down into the engine compartment.