https://www.sewingparts.co.uk/machines/nelco-221.html Do these look like the ones you're trying to track down?
the 221F may be different as the bobbins on this page are only 11 mm high according to the picture on the bobbin link.
The Nelco history page says that they are copies of Necchi and Elna machines and the ebay and amazon folks sell the necchi bobbins for elna and nelco machines. That doesn't mean they are really going to work for you if your bobbin is 7 mm high. Here's the history page I was looking at:
https://sewingiscool.com/nelco-sewing-machine-history/