Tom, for an electric mount you should not need much. A bicycle inner tube should have the right thickness.

A diameter of 2.3" means circumference of about 7 1/4". An inner tube with flat width of 3 1/2" should work, except I doubt you will find anything that's just right.

You can make your own. Here's how I do oddballs....I cut a strip about 1/4" longer than the circumference, with the correct width and thickness, wash it well and degrease it with alcohol or acetone, and prep the ends to be glued together. I grind about 1/2" of the rubber ends with a dremmel drum sander into a tapered section and simply glue the ends with rubber containing ca. You may use any ca, such as that for foam, as long as it stays a little flexible. Regular ca probably will work in an electric app since vibes are less.

You want the rubber band to actually stretch slightly when fitted. My early stuff required too much stretching and the mounts tended to be stiff. Now the stretch is minimal and mounts are better, absorbing vibes better.

Hope that helps. And btw, the last couple mounts I made for gas engines were done this way, and still holding strong. The trick is to expose fresh rubber. It sticks to itself with ca great.