250 csr sprocket help

[Wal1]

Front sprocket is worn on my 250 csr ,just checked the number of teeth and it's a 17 on the front and a 56 rear,from what I've found online it should be an 18 front and 55 rear, I can't seem to find these anywhere online,worst case is I'll leave the 56 on the back as its like new and so is the chain, can anyone tell me where to get an 18t gearbox one from though

[g80csp11]

sprockets unlimited can supply most things
http://www.sprocketsunlimited.com/Sprockets.html