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And here I thought he was just talking about US suspenders...

Yamaha makes braces that allow for the entire valveset to be removed.

Both King/Conn and Jupiter make tubas with removeable valvesets. The braces that they use have allen screws to hold them together. Check with a repair shop familiar with these and they can probably tell you how to acquire the parts.

Didn't Reynolds also use some sort of removable brace too? Seems like I recall a threaded boss attached to the brace flange,with the brace rod fitted with a captive nut. I probably even have a couple in my hellbox.

You might want to talk with somebody that builds or works on a lot of Thayer valved trombones. By the nature of the Thayer design, they require removable braces.

I'm not sure if pre-existing braces for trombone would be just the ticket for you, but they might at least give you an idea of what direction you want to go in.