I hear good things about Maximum Motorsports on 41 just south of 30 in Schererville. 219-322-6120. mxmmotorsports.com. I've purchased parts there (very knowledgable) but never had any service done there. I'd try them if it were my sled.
The local snowmobile/jetski/motorcycle dealer on 30 east of Merrillville is Maxim Powersports. They carry Polaris, Yamaha, Suzuki, Ski-Doo and Kawasaki. I've purchased several sleds there and had a stator replaced on a Polaris ATV for a very reasonable amount. I don't know how competitive they would be on a rebuild.
Also, for small engine repair I've had very good service and better than reasonable pricing at Gruel Brothers in Crown Point. I don't know if they do complete rebuilds however I would think they'd have to as they are a small engine dealer. 219-663-0076.
Good luck