I've seen only black ones in the catalogs .If you are really in need of some white ones and have one good one I know of a person in Ca. that can make some for you . He made some white ***** for the stock radio in the 1ST-RIDE .They were a perfect repo .
C&G has some, but they list them for 47-48 Passenger car I believe. AAMOF, here's a picture from their catalogue for a 47-48 passenger **** in gray. They have ivory, yellow, gray, tan and white. The colors are very subtle - almost non existant. I know the ***** you are talking about and they are the same as this only without lettering. I'd ask them. But this will give you a starting point.
Give them a call or visit at the link below. when you call ask for Kile(who is the god of parts knowledge there) and tell him you need the white ***** for a 48-50 F1 Fresh Aire Heater. He should be ble to cross check for you.
Both Dennis Carpenter and Mac's lists them on their web site but neither have a picture, LMC also lists them but their drawing is not of the correct style, so it would be best to call them and find out if what they have is exactly what you're looking for.