John,

I had a similar circumstance happen on a 50' Hi-Fold door on my hangar some years back.

Because of all the suspended weight these cables support and not wanting to put up with the possibility of injuring/killing someone or damaging property if I put in a substandard spec'ed cable, I ordered replacement cable from Hi-Fold Doors.

http://www.hi-fold.com/

Bet you that they can at least give you a good recommendation...I know they had all the parts needed to get my door working like a champ again.

Best,

Rob Schroer
ZAP