I built up a bike for my wife using an old Raleigh Super Course mixte frame (Reynolds 531 tubing), Sturmey-Archer AW, 700c rims, rear sidepull brake, front generator/drum brake hub, B&M headlamp, alloy VO fenders, an alloy chainguard, etc.
I guess what I'm saying is there are some cool old mixte frames out there, at good prices, and you can build them up however you please.