The issue withthe Big Radius that Vance & Hines is taking months to fabricate is a new mounting bracket, not any real modifications to the exhaust itself. The other post you mentioned has a member that has fabricated his own mount and is selling them as well. Since it is nothing more than a mount to the frame, I can't see how this could void any warranty but that is just my opinion.
As for other aftermarket pipes, your only bet that I know of today is with Cobra;
http://www.cobrausa-hd.com/category....=1&bmid=25. However, they are straight drag pipes and probably not what you are after. I don't see anything on their site specific to the Rocker but the catalog I was looking through at a shop the other day had a specific part number for the Rocker.
My impatient a$$ self has pretty much decided on some Martin Brothers and making a custom mount.