Vento avalanche ex100
 

Does anyone know where I can get a carburetor for a Vento avalanche ex100 please?

A picture of the engine would have helped. From Google it looks like a 90cc Minarelli engine, if it is a two stroke, that is what it will be. Apache, Polaris and a host of others used the same engine, so carbs for them may be easier to find. Most were electric choke, is yours?

It has a oil container near the battery, looks like it mixes the gas and oil. I don’t see a manual chock on it.

https://cimg3.ibsrv.net/gimg/atvconn...8f5d42f4f.jpeg
Oil bottle
https://cimg2.ibsrv.net/gimg/atvconn...cb2b373b2.jpeg
One side of engine
https://cimg4.ibsrv.net/gimg/atvconn...15ba86d4d.jpeg
Full view
https://cimg5.ibsrv.net/gimg/atvconn...ab6dd8704.jpeg
Other side of engine

Yes, that looks like a Minarelli engine. Bike looks in good order, and has an electric choke. Externally the carb looks OK why do you want a new one?

The bike has been sitting since 2013 and was left with a full tank. When I took it out of storage the gas tank was bone dry. I put gas in it only to find it all leaked out next day.

Now That's funny.
Clean the carb.

Someone was saying that because the carb is pretty cheap, it’s easier to just replace it.

I think that you will find that the original carb is much better than the cheapie your thinking of buying.
Carb cleaning is something that you may do a few times a year. Might as well tear into it. :)
Run non ethanol fuel.

Is there a rebuild kit I should use?

I remember OPT recommending "shindy" rebuild kits.
IMO, you don't need a kit, you just need to clean your carb. Dirt gets in, things get yucky. :)