Any aftermarket grips for a 1-inch bar will work. They are very easy to install, but if you get universal fit ones instead of Intruder-specific grips, you may need to destroy your stock grips to re-use the original throttle sleeve. I just put on a set of ISO gell grips on one of my Intruders, and it took about 20 minutes, including adjusting the throttle cable afterwards.
www.accessoryinternational.com has an asortment of Arlen Ness grips.
www.accessoryinternational.com has an asortment of Arlen Ness grips.