As mentioned already, find cantilevers that use post mount pads. I had an old CX bike with 68mm spacing and successfully ran Suntour XC-Pros and stock pads. You can add Kool Stop thinline pads for additional room if needed.
Most old higher end cantilevers are better than any canti offered today IMO, with the internal spring Suntours being the cream of the crop.
Here are some on ebay for a steal.