Longer lengths possible: I am sure yes; we have already seen demonstrations of 3 meters using cables extending the camera v1 board.
Available elsewhere: not yet, this was a custom part for this specific project. Nothing beyond straight-through 1:1 flex cables are considered stock items. If you want to search, look for FFC (flat flex cable) or FPC (flexible printed circuit).
But if there's a significant market for longer and/or cheaper product, I expect it will be filled, just as the various China-sourced ebay vendors have provided v1-compatible camera alternatives after the market potential was shown. I suspect the length of the official cables has more to do with passing FCC/CE EMC testing than usability. Wares from ebay are not so limited