you could do the the unthinkable....... walk into a shop that supplies renthal sprockets....... with your lxr sprocket and match it up.... the crf150's sprockets look quite close.... maybe a honda shop?
from what i could tell doing a little research the crf 50 ones may match, i think best bet is like loco said, take your lxr sprocket into a honda dealer and see what you can match up
take your old one into the honda dealer... just hold your sprocket as if you could throw it.... if they make any sudden gestures towards the mini community just tell him/her you can also substitute mini/lxr spockets for throwing stars.....?
if they have them hangin up on a rack in the accessory's isle, just match em up yourself!!!
if they ask if its for a pitbike, just say "i cant tell you, its a secret, now are you gunna help me or not?"
as arrogant as that is, it should get them off your case, ooorrrrrr you could tell them about our mini community! tell them they are more then welcome to have a squiz when they can, just to re-assure them we aren't delinquents riding around the back steets and trying to hit gigantic 60ft tabos and snap the damn tdr pro.
hope ya find some mate! you should report back if you find out!!!
Love Loco!