Try McCoy's. They closed their separate facility for repairs about a year or so ago, and I'm not sure if they picked up the slack in their main store. The Link
AAA Lawnmower on Burnet Road (just north of 45th). I took mine in about a year ago, and was very satisfied. Only problem was it took about two weeks to fix. They did warn me they were backed up and it would be about two or three weeks.