Unless you want to fully DIY,
this may be what you're after. I used one before I made my own wheels/shifters/enclosures and it worked well.
Or maybe you want something like
this or
this? In the case of the last two, you'd need an adaptor to attach it to your wheelbase.
Premade adaptors
here, or get one of
these 3D printed.
Also, have a look around
here and see if there's anything that fits the bill.
ED; or do you mean that you somehow have a GTE rim and need the button/shifter enclosure that's meant to come with it? If so, I think you're out of luck unless you can find a used one.