Hi there, greatoldone,
I too had issues getting one rusted stud out of my manifold, but I did eventaully get it out.
If you have part of the stud still protruding, try clamping this bit in a large vice and then grabing the manifold in both hands and rotating it.
If not I would try ebay, as i have seen them for sale from time to time.
Or there is these guys but I have not used them myself...
http://www.fabdirect.com/index.html
I have a spare inlet manifold, if anyone is interested, but I guess that's not much use
all the best, Peter