Sharon, with exception of kits like Polaris, Sierra, Elegant Beauty, buy bushings with new kits. Hate to refer you to library for bushing compatibility chart, but it is a good reference. I use catalog or web site.
Elegant American, think is a Berea kit and requires 15A or 17B bushings. Not sure what Berea re-sellers call that pen kit. Doubt those bushing compatible with kits mentioned in this thread.
I would buy bushing with PSI Executive kit, or Polaris. Polaris twist and click take same bushings. They offer an Executive 8 kit special for $66.15 + shipping.
Berea has an introductory offer on Retro Pen24K upgrade gold kit buy 10 and bushings are free. My catalog list $44.00+shipping.
Craft Supplies American Classic, has no specials.
Berea & Craft Supplies extra tube little cheaper than PSI. You can use PSI extra tubes on both Executive and Polaris but require you cut to size.