Do you hang out at LFPF? Chances of getting one are better there. The downside, you have to be a member there minimum 30 days before they let you access the ads. Of course, if 4x5 would do, I can hook you up for a reasonable price.
do you have any idea what lens you want to use with the format? Since you're aiming for portraiture, that would push me to think you're not thinking "field" camera but rather something like a Sinar in a modern camera, or an older Agfa/Ansco or Burke & James for a classic camera. There are some older Agfas that take a 7" lensboard that will let you use some of the bigger barrel-only classic portrait lenses. If you're planning to shoot modern lenses in Copal shutters, then sticking to a modern monorail like the Sinar makes sense.