The cable is usually a sealed unit and once it is seized you have to replace the whole thing.

When I changed the cable in my old boat I got a replacement from Whitworths. They are a pretty common, I would think most boating shops would have them.

Sometimes they seize in the steering arm rather than the cable itself. Have a look at the cable near the motor any bulges in the cable then probably needs replacing.
How long since last used - have you tried putting a bit of wood over the end of the steering arm and giving it a whack with a hammer once moving a bit of grease may keep it going a bit longer.

I used to have the same boat but with a johno on the back.  I got mine done at boat city wasnt a bad price from memory.  I noticed with that particular motor I had to keep the steering arm oiled and give the steering wheel a couple of rotations every couple of weeks when I was running the motor if I wasnt getting out

gotta keep them moving over winter,or they sieze up

had the same thing happen a few months back , greased it and was stiff as buggery backed off the nut at the start of the arm and turned out had an air lock in it , smooth ever since

My steering cable broke last year and needed to be removed and replaced. My mechanic suggested strongly NOT to use grease, as it will go hard and it actually can cause the seizing. His advice was to give it a squirt of oil on the exposed end and then to turn it lock to lock a few times to distribute the oil. He also recommended leaving the exposed end extended (out) when parked up. It's working so far!

I just installed a new cable on the weekend.  Mine was actually snapped at the outboard end.  Check to see if its the end of the cable rod as that frequently greases and "gums" up, especially when exposed to the elements.

Its usually where the end of the cable comes out of the tilt tube.  If you do free it, use oil as grease can clog it up.  Lanox is meant to be good.  White lithium grease spray good as well.

If the cable is siezed internally (don't know if this scenario is common), you are up for a new cable.

Check at the outboard end and you will see alpha numerics engraved onto the black tube.  I believe the last 2 digits are the measurement in ft.  I just researched mine as it was an Ultraflex and found Allboats to be a dealer for them.  They promptly ordered one in and everything was good.  I kept the same helm as it was a non feedback one.  You can get a whole new kit with cable, helm and bezel but might as well save a few bucks.

Installation was easy. Make sure you take time cleaning out the crap in the tilt tube before sliding the new cable rod through.

Couple of good youtube vids to help.

Hope this helps

Chris

 Looks like a new cable is in order will drop into all boats today and see if they 

have any in stock.thanks again for everyone's input

 $389 to replace my seized cable at dinghyworld last year.