Custom Phono interconnect build-out shops or vendors?

Talk to Paul Speltz at Anti-Cables. They’ll build anything you want for very reasonable cost, to include wires and connectors.

Try VH Audio. Chris can build you anything you want at reasonable prices. 

Also, a fellow member ,(williewonka)

Triode Wire Labs does plenty of one-off wires of all sorts.

Check the link I gave you in the first answer, Frank at Signal Cable will give you the best value for money, really doubt you can find anything better, custom lengths for all his silver phono cables and connectors of your choice (XLR if needed).