There are several different brands of clear coat spray on the market and most of the model paint manufacturers have their own product. You should be able to find clear coats at your local hobby shop, if that fails, try any number of hobby suppliers on the internet under their paint catagories.
There are flat, semi gloss, and gloss sprays so you need to determine what is best for your model.
I prefer to use the Floquil flat spray in a can as the oder is less potent than Testors dull coat for a flat finish. and it works great.
A lot of modelers use Future floor wax for a gloss finish over decals....and to apply them. But I don't see the extra step is really needed. AND if your decals don't come out right, or you need to change them, it's a real mess to fix when using the Future...
Hope this helps !