Mel:
1. Welcome to the forum
2. Where are you located?
3.
http://www.winnisquammarine.com for parts
4. I agree, sounds like a broken cable if you can feel no tension at all. If its in gear, it should prevent it from starting as previously stated. The only other variable I suppose would be that the cable came off of the linkage either at the drive side or even at the throttle control side. Before I ordered a new cable, I would check both ends. In terms of replacement, I bet you could do this yourself, fairly easily. If its determined to be a broken cable, just unhook one end and use electical tape to secure your old cable to the new cable. Pull the new cable through while removing your old cable. This should handle getting it from one end of the boat to the other without too much hassle. Connect it and give it a whirl.
Good luck!