I'm guessing that the reason you don't see them is they are really not necessary. Drill a 1" hole directly in front of your valve stem, at approximately the 9 o-clock or 3 o-clock position. Buy a 1" chrome snap plug and a valve stem extension. Put a mark on your tire at 6 o-clock when the valve stem is aligned with the hole. Simply snap off the plug and insert the extension, screw it on, and you are all set to either check the pressure and/or add air.
I did this on my old original wheel pants, but when I went to the "Dolly Parton" wheel pants, I also went to the "air-stop" tubes. Now I only have to check tire pressure about twice a year so I just pull the front half.
I've got the same 1" holes Randy describes on my 6A with old style pants. They work great! Airstop tubes will be installed at the next condition inspection, I've used them on several other planes and they are a marked improvement over standard tubes.