Where can I buy attachments that will allow me to fasten my full size headboard to my queen size bedframe? I am having a bit of trouble finding one.

Some furniture and hardware stores sell kits known as "Mod Plates." These can be used to attach a queen headboard to a double frame or the other way around. If you have a headboard that required side rails (as used with a footboard) there is a different kit that has hooks on the plate. These plates bolt to the frame and the hooks point up, so you can hang your headboard on it.

Best Bet Mattress Shop That Sells Headboards They Are Called Adapters Cost About $10