Actually as I found out yesterday, most exhaust shops have the dies to make the joints (they normally come with the pipe benders). All that is needed is a pair of correct sized flanges which most shops should also have.

Many of the stock 70's exhaust systems also had them built in to the pipe (I had a spare pair I had set aside to take with in case the muffler shop couldn't make them. I usually save them when I come across them in case I'm building my own system or want to put a set in when I have to cut a pipe to access something.