Just click on kurveygirl or STG add above and get some new pads. For example Kurveygirl has Versah XX for M50 calipers for $147! Buy new, support sponsor and don't gamble with your brakes...
Can't argue with that I guess! Quick question, maybe it's me but why does it seem so difficult to confirm fitment for the M50 caliper? For example, the pads you mention on KurveyGirl, they're titled as being for M4 and M50 calipers but in the fitment chart at the bottom they don't include the M50, WTH? https://www.kurveygirl.com/shop/product_info.php?products_id=468
I can confirm the pads in the link will work with M50 calipers. I run the exact same setup. Its a great price!