Try this site, not as good as minorleaguesplits but will still get you what you need:
http://mlsplits.drivelinebaseball.com/mlsplits/playerinfo/446395
Corey Brown's splits from AA 2010:
vs Left: .266/.355/.435
vs Right: .356/.455/.546
Thanks. I'm less impressed with his power against LHP than against RHP, but that figures. The OBP v. LHP seems to bounce a lot, but in any individual season, it seems to be influenced by small numbers. That said, both years in AA he seems to not be weak against lefties.
how much do you trust major league equivalents? I'm interested in how the kid will do when he makes the majors, not so much how he would have done had he magically been plunked in the majors when he was playing in rookie league. MLEs I'd think are more useful at AA and AAA when the kid is close.