Belmonts Rod & Custom should have what you need. He has an ad in Hemmings. I sold him a whole bunch of NOS M/T and Mr Gasket a few years back. Also, You can still buy these new from Offenhauser-you have to go through one of their distributors. Some of the street rod vendors that deal with new nostalgia parts still sell these from Offie. Hot Rod & Custom supply, Obrien truckers, Patricks, Speedway
www.speedwaymotors.com (402-323-3200) etc. Check out
www.vintagespeed.com I think they have them also. Sorry I don't have the other numbers they only sporadically advertise in Street Rodder
Don't wast your time with Summit or Jegs-the young rice burner salesmen won't have an idea what your talking about and Summit Jegs hate to special order small stuff like this.
Hope this helps.
Dave
Speedway has two types of offie breathers in stock your looking for but they are not exact. I will check in my offie catalog tonight and get you the correct part number. They make about 20 different vc breathers in this design.
Hot Rod Vintage Parts
www.hotrodvintageparts.com is also an offie dealer.