I just saw Farncombe Pop's post on NSRA site, looking for a cable for Jag IRS, I think you're sorted now?
Anyway, I found that a Morris 1000 cable was perfect for the job, (on my Pop). it even has a built in bolt, so you can fix it to the chassis.
My handbrake was still 'kin useless, but the cable worked a treat!!
There maybe other cables suitable now, but back then, that was the best fitting one, correct length too!!