Just about any 1-inch handlebars will fit the bike. Intruders have come with several different style bars over the years, from drag bars to 2 or 3 different style buckhorns. The best thing to do might be to go to a local shop and see what they have, or sit on the bike with your hands where you want them and have them measure the pullback and width so the new bars will place the grips in the right spot.
However, the install is a real bitch, as your early Intruder uses internal wiring: all the control wires are run inside the handlebars and risers. You have to carefully de-solder the wires from the control boxes, and pull them through the bars as you remove them. You then need to drill the new bars with the correct size holes in the correct location to match the old ones, then pull the wires through the new bars and solder them back onto the control switches. It's a real pain in the butt.