So I found the maker of that single high pipe. Ixil. It's the first pic. It retains the original header. It uses a three bolt joint to clamp the end can onto the link pipe so you could fit any cbr900 can onto it.
That ebay link is for a seller in Aus. He might separate and just sell you the link pipe. He's had it up for sale for almost a year. Let him know the end can will fit a cbr900 setup.
Or maybe email Ixil?
The other pic shows a custom made 2" link pipe with a standard 51mm can and clamp. I think this would be a good option for you. Take your bike to an exhaust fabricator and get them to bend/form a 2" link pipe for you.