According to
the product page on 221 systems, they are using an oilite bronze bushing. Although a specific McMaster-Carr part number was not listed, something that fits the dimensions of your designs can surely be found
on McMaster-Carr. I wish you the best of luck in your swerve project. Don't be afraid to post here for more help if you need it, and be sure to post the final results to show what you've done at the end of the offseason! My team isn't quite ready for swerve at the moment, and I always get a little bit jealous watching non-tank drive robots glide around the field effortlessly, although our WCD wasn't too shabby this year.