The only one I know that is being reproduced is from Jim Carter. The one I use that looks more modern (works better too) is a NAPA 2373. If its original look you are going for:

http://www.oldchevytrucks.com/cart/product.asp?prodid=ME238&i=|Air%20Filter|||54|

Deve

1950 Chevy 3100 Deluxe Cab
1950 Chevy 3100 Standard Cab
In the Stovebolt Gallery
The Think Tank
More info and tips at Deve's Technet