Scott, I spent a year and a ton of phone time chasing down leads on possible makers in the US including makers of hydroformed bicycle frames, guys who had made these exhausts in the past but no longer did, and anyone else who might be capable... The only one I found was Rob North in Southern California and he was booked up on other projects for years. Finally went with my German friend, Thomas Quast, to a small maker in Switzerland. He produced three sets: one sold to Australia, one kept by Thomas for his ungoing Seeley project, and one set that I have. They were not hydroformed, which IMHO aren't smooth enough, but rather hand-bent. No, they're currently not for sale. My set are still slated for my long-term MV 861S/Magni/CB750 "tribute" project.
You can see videos of the pipes mounted and running on my old Read-Titan Daytona on classiccyclecity.com. They sound incredible!
Given the difficulty of doing these domestically and the cost of them in Switzerland, the deal in Spain doesn't look too bad. I believe that Menani also makes them in Italy but they are generic in size and shape so fitting them would be a catch-as-catch-can proposition. Good luck!
RR