Downtube Shifter Mounts?

Gday mates,

Wondering if anyone could point me in the right direction?, I am trying to find a 34.9 downtube shifter mount.

I know problem solvers and some other brands have 31.8/28.6 clamps but I need bigger!

It’s an aluminum 650b frame I’m trying to slap this drivetrain on that for some reason only has one braze-on cable stop on the downtube - it’s effectively 1x only and I don’t like that.

I know I could probably run it suicide shifter style on the seat tube like what Russ did in that PLP video, but I want to run brifters on this setup.

Is there some other sort of shifter boss add-on kit out there that would work for this kind of thing?

Any ideas greatly appreciated.