I managed to get eight working chips for an MB6582 at the tail end of 2018, and they're still working (touch wood). It was not cheap.
got several from these two sellers (below) on ebay which were all working fine. Took a while for them to come up though. Will let someone else comment on clones! https://www.ebay.co.uk/usr/splat79 https://www.ebay.co.uk/usr/commodore_mark1