An easy solution is to read the length of the belts & simply contact a bearing supplier and ask for the belt/s you want either singly or as matched pairs
https://simplybearings.co.uk/shop/Be...oaAp9BEALw_wcB
The closest to am 11.9mm belt is an SPA section belt 13mm wide & this will sit proud of pulley . So for an example you could end up asking for SPA 980 matched pair , the knowing parts person will simply waft away & return with your requested items . Result = Happy days