I just took my throttle cable to an old motorcycle shop (by old, I mean the owner is 72 and he has been in business since the mid 70s.)
On a side note, he still rides and races every weekend... Man, I hope all of us can be that way!
Anyways, back to the throttle delima.
Mine was buggered up somewhere in the housing and wasnt allowing the cable to slide back and forth. A new cable was priced to me for 169.99. My bike shop guy repaired it for 20 bucks!. Just put it in and it works perfectly too.
So, I would suggest taking the cable to a good bike shop.... see if they have a way of rebuilding it for you.
I would suggest "older" shop too....because those same type cables were the life-line of older dirtbikes.
Good Luck.