Two US sources carry many discontinued film sizes. Chicago retailer Central Camera sells fresh rolls of film in sizes that are no longer available elsewhere. Prices are listed and Central Camera provides a toll free number for orders. 127 and 620 film comes in color print, color slide and black and white. 126 and 128 available in color print film only.
Processing is also available.
Order by mail. This is not quite as simple as it sounds. Wear cotton gloves and work in a clean environment. Attach the end of the 120 film to the paper backing with masking tape before you start respooling the film and paper backing on the 620 spool. You may need to adjust the piece of tape which holds the film to the paper backing at the start of the roll.