I was wondering if anyone knows of a company that produces a performance
MAF sensor for the Xterra. If any body has links for other performance accessories it would be great.

What exactly is a "performance" MAF sensor? The OEM one isn't restrictive.

I had a 96 GMC pickup before my xterra, and they had "performance" sensors that were just larger. I was just wondering if anyone had seen anything like that for the xterra.

Sure you're not thinking of the throttle body? A larger one of those will allow more air in, limited by the restrictions of the intake itself and by the restrictions of the exhaust, thus resulting in more power, but probably not really cost effective by itself.

http://www.granatellimotorsports.com/product_display.php?gid=275

Something like the one in the link

Personally I wouldn't bother with it.