Baxter,
There was also a firm in Oakland that specialized in porcelain manifolds, but not sure if they are still in business either.
Anyway, did both my 37 LaSalle and my 38 65 Series Divider window 5 passenger and they are great. Oh, the name of the firm is Prairie Auto Porcelain, Phone: 507+334-9309. They are in MN. I have sent other folks there and all have been happy with the results.
John Washburn
CLC #1067
Remember the Turlock Swap meet is on the 28th and 29th. That one part may be there waiting for you, so dont sweat the cold or rain.