Reason to repost a photo of my commuter!



Salsa Casseroll would be a good choice but they no longer offer the single... you'd have to get a frame and build it up.

There are dang few production bikes with forward horizontal dropouts, room for big tires and fenders, caliper brakes, and offered as a SSFG.
Not sure why you wouldn't want cantilevers but that's what the Pake has... also just a frame.

Masi reviews on my blog.