small semi-rigid coax with air dielectric

Possibly this question should go under hobby...
Does small semi-rigid or rigid coax with approximate air dielectric exist? I'm thinking of a diameter to the nature of 0.047 inch for making baluns and impedance transformers. The lower z would make it easier to go up in frequency.

I see larger cable using a spline to support the center conductor but do not see it in a small diameter.

tnx,
GE

The thinnest Spline dielectric coax cable that I've seen is about 6.3mm (0.25 inch) external diameter.

Yes that is also the smallest I've found. It must be too difficult or expensive to manufacture.

An air dielectric coax has limited bending ability.