In terms of longer cables, they are readily available in lengths up to 6 inches fro Digikey. For anything longer than 6" you have a few options:
- Build a small "bridge board" with two flex connectors back-to-back so that you can chain together two cables.
- We have successfully (albeit slow work) soldered three cables to each other to make a longer cable.
- Finally, you can customer order cables from the manufacturer, Parlex (Johnson Electric). They have a minimum order quantity of 4,000 pieces and their leed time is 10 weeks.
We do not specify a limitation on cable length, just that capacitance of the line should be <= 30pF.
It may be possible that there are other suppliers such as Molex or Wurth Electric but I don't think they have stock available.
Here is a link to buy the 6" ones from Digikey: https://www.digikey.com/product-detail/en/parlex-usa-llc/050R4-152B/HFF-04U-06-ND/660037