If you don't mind me asking, what's the gift? Because he has a girlfriend, it would be inappropriate to give the guy a stuffed bear with chocolate or something that can absolutely be interpreted as romantic. For example, I was already dating someone else when this other guy kept giving me red roses. It was the most painfully awkward thing ever. It put a damper on our friendship for a long time (despite being pretty good friends for a few years), so be prepared for that if your gift can be interpreted that way. I personally don't recommend giving him a gift if this is the case.
If your gift is something that is not romantic, then by all means just give it to him in person. Don't do any weird gimmicks like finding his locker location, his schedule/house, etc. It'll lead to him thinking you're creepy, especially since you're still establishing a friendship. Respect his boundaries in this stage.
Good luck.