I have never myself seen them for sale as such. Rebuilt my nitro trailer last year and just purchased two salt treated 2x4's cut them to length; drilled bolt holes as needed; cut two pieces of carpet and used a air compressor stapler to attach the carpet. Put your carrage head bolts thru the hole before attaching the carpet. Wasn't hard at all and took very little time.
AC
Aspire to inspire before you expire.
When demostrated a flame thower for the first time, Chesty Puller looked at the weapon then asked, "Where the heck do you attach the bayonet?"