If you like light aluminum sticks, the Murray Pro stick is great but it's $80 USD. If that is what you broke, I have had NO luck finding the raw stock to replace just the inner tube I always break.
Here is my fix. Save the end plug from the Murray that pins to your crossbar. Get a boat hook from West Marine and remove the hook. It is good quality aluminum and the outer tube is the bigger one. This allows you to wrap it for better grip. I use hockey stick tape - cheap, light, and waterproof. The plastic plug fits EXACTLY. Two rivets and your done! You can break 3 of these for the price of a new Pro Stick!
You can also get a boat hook that is EXACTLY the Murray core (made by Davis Instruments) from SailNet for $22.50. I haven't actually seen this one but the description looks right.
http://www.sailnet.com/store/item.cfm?pid=21596