Not to be a complete idiot or anything, but why would you want to use a viewfinder camera for shooting closeup? The days of focusing frames for, e.g., Kodak Instamatics, are long gone.

When shooting closeup there's really no substitute for a camera that allows focusing and composing through the lens. For mobile subjects, including flowers that blow in the wind, an SLR is ideal. A view camera will work for static subjects.

Shooting closeup is challenging enough that there's no reason to hobble yourself with unsuitable equipment.