polini does indeed make mufflers for minarelli engines. or at least they did. i just got three of them (two standards and one custom two-piece) for myself and two other moped army members ... along w/ a leovinci cut for the minarelli as well.
but i do have an italian moped parts connection in italy ... but check around. they are there. let me know if you are truly desperate ... i might be able to help you out.
but i played w/ their website. the parts are there. those are the mufflers we ordered from them. you should be able to email them w/ the name of the exact part (or call them) and order it shipped to you. most of the site is in english ... so it should be ok.