Hello,
Just picked up a Cox.049 Cosmic Wind. Engine is seized. I need to either pick up a complete engine, or just the piston and cylinder. I looked on ebay and did not see the same engine. Most had the fuel tank attached to the engine. Can somebody send me a ebay link to what engine I could use, or maybe the correct piston/cylinder I would need.
Thanks for any help you can provide.

http://coxengines.ca has parts or whole motors. You can likely free up the motor by removing the plug and backplate and soaking it in fuel for a few hours, and rocking it back and forth with a prop on. While it is apart, make sure the reed is moving freely and the needle valve is clear of old dried up oil.

Remote, these engines are easy to work on. Perfectly normal to get gummed up after a long period of not running. Clean it up with some fresh fuel and reassemble. I'd bet you don't need a new engine.

A little heat from a hair dryer on the cylinder usually frees them up in a few minutes. Just install a prop and heat it up till it is just a bit too hot to hold for more than a second or two, a little pressure on the prop will usually free it up enough to get a couple drops of fuel into the cylinder. Then you are good to go. As someone else mentioned, make sure the reed is free before you put it all back together.

I think there are youtube videos concerning this issue, you might check it out.

Another source of COX engines and parts here in the US is EX Model Engines.

Just a word of warning - don't use too much force trying to get the piston to move. Let the fuel dissolve the dried up oil.
The connecting rod is ball ended in the piston which is 'peened over' to hold it in place. Pull down on the connecting rod too hard and you run the risk of actually opening up the little end - then you might indeed find you need a new piston assembly!