Rotary table with 3-jaw chuck
For milling circular features on the Bridgeports.
Should be able to mount on the bottom or side.
Price is for a new Shars 8" rotary table with 3-jaw chuck, but from their ebay store (cheaper): https://www.shars.com/8-h-v-rotary-table-with-8-3-jaw-chuck
Or, could wait and find a good deal on a used one for less.