Pat,
The CL Bartlett is a nice machine at a great price---don't think it will last long. It uses a 20x1 needle also known as Eldredge flat shank or Boye 14. Most likely it uses the National / Eldredge short shuttle or Boye 13.
$25 for a treadle in good shape is a no brainer. Sort of tempted myself to hop in the car and head to Dover, DE --well almost.
Good Luck
Jon