I'm surprised they {drs} aren't more concerned about the extra c ribs? Do they show up as small or an incomplete set?
{some will have a large or full set and some only partial set}

I always thought in most cases extra c ribs were a definite positive for TOS if the symptoms fit also.

If you aren't in high pain or constant pain they may not want to risk doing any surgery yet.

I would call around to hospitals or dr offices and ask lots of questions to try and track down an expert surgeon or doc that has a firm knowledge of TOS.
Even PT places and therapy rehab places might be of help with that kind of info.

Is there any of the advanced imaging places in the area?
3D MRI or MRA? I might have the names wrong or maybe there is another one I can't recall the name of it.