Is there aftermarket camshaft for the 3.3l supercharged engine?

I can't find any either. There isn't much of a performance market fo the xterra other than off-roading. You could do a smaller supercharger pulley. Check this out.https://www.4x4parts.com/c-1057001-nissan-performance-pulleys.html Alex

Contact Crane Cams - they'll grind you one ! ... Highly recommend thorough research on all mods specs.