The straddle cables on my Dia-Compe 960s are 220mm, or thereabouts. Same as on my Dia-Compe 980s. As far as I can tell, nobody makes this size anymore, so they are hard to find. The straddle cables for centerpull calipers that I have able to find are all too short. Longer straddle cables, which can be purchased from a variety of on-line sources, tend to run 330mm - 380mm and are likely to be too long. (I am able to run one of these on the front of one of my canti-equipped bikes, but not on the other, and they are too long for the rear brake on both bikes.)

If you can't find the right length either used or NOS (I'd check with a couple of local LBSs, if you can), then you could do what I've done. Buy either a single-ended or a double-ended straddle cable that's too long, and install a new barrel end at the point that will give you a cable of the length you want. If you're handy and can solder, you can probably do it yourself. If, like me, you're not that handy, these things can be purchased on ebay at http://cgi.ebay.com/brake-straddle-c...item3a64c73c5a. $15 per pair, IIRC.