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The short answer to your question is that it's been released.

I don't know of any in the United States, but I played one while in Europe. It's basically a 45slp with an extra valve setup to play as a 4 piston + 2 rotor tuba. It's also gold lacquered, for what that's worth. I liked the one that I played, but it was a little akward since it was a 4+2...maybe it wouldn't bother you.

It's the new Mel Culbertson model. He's a B&S/VMI/Meinl Weston/Melton/Whatever it is music group artist. This tuba is designed to replace the VMI Apollo F tuba that really just kinda sucked.

It's a good tuba, but you'll be hard pressed to find one in the U.S. If you want one bad enough, I'm sure Dillon's or Baltimore Brass (among others) could get one for you.

I'm sure what model you saw that was 4 piston +1 left rotor and 2nd slide kicker.

It may have been one of the strange Hilgers model Meinl Weston F tubas...they have so many valves and slide triggers on them that you about need 4 hands to play one. The only thing is that all the Hilgers models are rotary valve horns.

Meinl Weston has a number of options for their tubas, so maybe you saw a custom ordered tuba:

Gold Brass Bell
1st or 4th valve trigger
Detachable Leadpipe
Viennese Valve System (3+3 and "rearranged," usually)
Qunit valves
Thumb 5th valve
Detachable Bell
Detachable Recording Bell
BBb Slides for CC tubas
Silverplating