Niagara falls you won't find anything on craigslist. And if it's fixed gear related, I'll get to it before you.

I would say go to some bike shops, I only know St. Catharines ones, and ask what it would cost for them to build one for you. A lot of the shops have old frames laying around, and they can order parts for you.

Most of the fixies around town are road bikers doing extra training. If you ever get one, hit me up, I'm always down for riding.