you need 0.5 mod, you could get them from wim at
http://www.actionmodelcentre.com/
or from rw racing direct
http://www.rwracing.co.uk/contact.html
best sizes in my opinion are 12, 13, 14, 15. they will give you options to try different ones i use 14 in mine,
dont forget to mention they are to fit a 2mm shaft