According to Cytron website, it stated "
11 teeth sprocket (#25 chain size)", if your bicycle chain is also #25 size,
it should be compatible, because it is the imperial standard that globally and commonly used.
Special hardware shop selling belts, pulleys, sprockets will carry the stocks, for example:
http://www.bangkok.com.myOnline reference link -
http://my.misumi-ec.com/asia/ItemDetail/10300431140.htmlNote: You mention the "Gear" is actually is called "Sprocket"