I got my center release buckles http://www.owfinc.com/hardware.html -- part GCR3/4. The ones from Quest look identical. They work just fine.
I also got my gros-grain from OWF. Be careful about using gros-grain from your local fabric store, since gros-grain refers to the weave and not the material. If you buy from one of the outdoor suppliers like Quest or OWF you'll be fine. Even with the gros-grain from OWF, it is thin enough that it crinkles under the center release buckle; it works just fine, but you have to be a little deliberate when you slide the buckle along the ribbon to not let the ribbon scrunch up.
I posted photos of my quilt-to-pad system, here's the link in case you missed it.
In that post I focused on a double quilt, but should have said that the system would be great for a single as well. I've got a Nunatak single quilt, and it uses the same materials (gros-grain and center-release-buckles) to pull the quilt together underneath you -- but IMO it's better to attach it to the pad instead so it doesn't migrate when you roll.