I'm not sure how unique the group is on the Bezzera (meaning I don't know if it is compatible with generic E-61 portafilters), but a quick look at 1st-line turned up
this one for the Bezzera. I have the E-61 equivalent (
link) which works great on E-61s (and so-so in Rancilio).
EDIT, I think you can use a Pasquini Livia portafilter, here is another at Chriscoffee.com (
link).