where to buy a coaxial of 25 ohm and 10ohm?

I want to constuct a transmission line transformer with coaxial ,but it seem that the coaxial of 25ohm and 10ohm is hard to buy. Can anyone tell me where to buy?thanks!

Answer to wrong subject ..

There are a lot of companies that make 25 ohms or 10 ohms coaxial cables. Especially semi-rigid cables. If you were looking for a PA matching application semi-rigid would be fine.
http://www.haverhillcable.com/

Also microcoax www.microcoax.com produce semi-rigid coax with Zo<50 Ohm.

But, for my opinion, Zo=10 Ohm look too small.