@cestrangio , Christopher use the links below, 1st link is Sony parts page where you could inquire about availability and the other links are belt suppliers that may have a suitable replacement for your M430. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
https://esupport.sony.com/US/p/model-accessories.pl
http://www.thevoiceofmusic.com/catalog/tape_rec_belts.asp
https://www.kenselectronics.com/lists/belts.htm
http://www.gbaudio.co.uk/data/belts2.htm