Okay I finally made some ground trying to find sprockets, there's SO many of them online :\
I pulled the following numbers from the Renthal site, just plugged in the '11 CBR250R:
Front sprocket: 368-520-13P (noticed that Aufitt used a 13GP, which wasn't listed on the Renthal site)
Rear sprocket: 211--520-40P-HA
Tried eBaying the above parts and got pretty much nil, people don't generally list the part numbers in the titles of their listings, which made it somewhat frustrating. They also make a habit of using the same generic image for all their sprockets, so I'm seeing several different sprockets for different bikes all starting with "287" which doesn't help. Tried Googling the part numbers too, to no avail.
Phoned up a place just down the road, these are the prices I was quoted:
368-520-13P @ $24.95
211--520-40P-HA @ $89.95
Gold X-ring 520 chain @ ~$135
That rear sprocket raised my eyebrows, is the price of that one so high because of the HA (Hard Anodised) suffix? I forgot to ask but was there a non-HA equivalent, and what was the longevity comparison? Second to last question would be to Aufitt, what model number was on the rear sprocket you purchased?
Final question also goes to Aufitt (or other Aussies that have changed gearing on their own), did you buy from a distributor or was it through a bike shop that had their own distributors? The former option would seem to be cheaper, however the only Renthal distributor I could find (via Renthals website) was Cassons PL, which are a NSW based company and after a bit of searching didn't have much in the way of 40t sprockets, let alone the 211 I was searching for.
Apologies for the long post