50 ohm board

Does anyone sell 50 ohm trace with the ground on both sides of the trace (vias)? I'm needing some material good to 10GHz.

Do you want a PBC with SMA connectors? You should do it yourself.
Only you know how close you want the grounds to be to the trace, or
how many wave lengths(how long) you want the trace. Or how think or thin
you need the trace to be (Dielectric constant, smaller = big trace, big = thin trace).

ExpressPCB is fast and cheap, but you will need to know the dimensions that
make a 50Ω trace.

Everything you need is on google.

Element_115, all you say is correct but when working with moderate RF power ( <+15dBm), trace thickness is a very low priority. The dimensions to achieve 50ohms limit the possible combinations (to a large number). Softboard such as Rogers & Taconics can be easily cut with an Exacto blades. Trace material such as this would be handy for prototyping attenuators, limiters, detectors, etc. I've worked with PCB express and a few others before. It's common for hardboard prototyping.

What are you actually asking for, what do you mean with "Does anyone sell".
It's a usual RF PCB design technique (surface coplanar strip with ground plane) .
It's up to you to use it in your design.