The only ones are made by AMD. The early production ones were not made so well where the gasket did not line up to bolt holes. The later ones were corrected. Jegs or Summit racing sells them and have very good return policy. They are pretty accurate. I had to get them because I had a hard time finding a good original 1970 vc. Ebay has them listed, but I have no idea if you would be getting an early production one.
Original ones come up on Ebay and other places. 383 and 440 are vc are the same.

http://www.summitracing.com/parts/amd-335-1070-bp/overview/