These replacement ribbon cartridges are compatible with a variety of POS, calculator and typewriter products. Cheap Printer Ribbons, Buy Quality Computer & Office Directly from PrinterField. I use printing calculator ribbons rewound on original spools.
https://printerfield.com/products/printerfield-compatible-typewriter-ink-spool-ribbon-for-calculator-olivetti-gr4-for-olivetti-typewriter-red-black