Welcome to the forum! You'll find lots of information on here and the people are very helpful.
it is most common to put it on the rear tire, because it is more convenient and you dont have to worry about a lot of weight on making steering awkward.
i would recommend this dealer: bicycle engine kit, bike engine, bicycle engine, bicycle motor
i believe he ships worldwide, but might not offer a warranty outside the United States.
if you do a google search for FRICTION DRIVE BICYCLE ENGINE KITS you should find a lot of sellers.
let me know how it goes.