I posted the link twice to where you can buy them. The metal panel is a perfect fit in the GVR4. There are tons of other products out there but a lot of them are shoddy and require you to use things like double-sided tape to mount them. This one snaps firmly into place.
Oh ya, and here's a slightly better picture of the plastic Omori panel. Again I don't think this one will work as well in the GVR4 because it doesn't snap into place but rather requires one of those DIN sleeves to be installed.