You can order one from Venture Electronics:
https://www.veclan.com/engappliance_sel_one?eng_ApplianceVo.eac_id=16
The order form has specific lengths, but actually the cables are all custom made to order, and you can tell them the exact length you want.
^^
I've ordered a 50cm mmcx to 2.5mm balanced cable from them. The cost was $29 including e-packet shipping to Norway. You just need to contact them in advance about the length if it's not listed in the menu.
My cable is in transit now but I'll post some pictures og it when it arrives.