Replace the dowel pin where the shift linkage attaches to the transmission. There IS a "bolt" or better known as a dowel pin that connects the shifter rod to the transmission. If it wears or moves out of place, then it will feel REALLY loose side-side. It's under the car, right in the middle, and at the back of the transmission. The part is $7 at the Honda dealer, and you'll laugh when you see the part.

There's supposed to be a round band/clip kind of thing that goes around the dowell pin to cover it up and keep it from falling out, but many mechanics "forget" to put it back on there after doing a clutch job. Maybe that's missing and it's falling out, or maybe someone used the wrong $#!† to put it back together.

EDIT: Get someone to move the shifter back and forth while it's in gear and see if you see it slipping at that point that I just described. Don't bother with jackstands or anything, just park over a ditch or something so you can get to it easily or crawl up under it while it's not running.