Keep calling, Many window companies won’t want to do the it because of the framing work involved. You might have to find a general contractor. Getting a permit for a header can be a major pain, your header is probably not long enough.

+1.

Between the single window aspect of things and the complexity, it is going to be less appealing to a lot of folks.

I think Todd is right in that a GC might be the way to go if you don't get traction. Permitting in FL can be a real pain for just windows already. Adding a structural component probably raises that pain.

If you can live with the current width, replacing with a taller window is a lot easier because you don't have to deal with the header.

In addition to tearing in to the wall to reframe, you may need to remove siding so that there is room to install new flashing and waterproofing membrane. Also be aware that, if you have any electrical wiring or venting near the existing window, it could involve more work rerouting around the enlarged window opening.