FORTRAN was never a major language on Windows, I'm afraid. If there are any free FORTRAN compilers for that platform, I don't know of them. I believe Intel had some products, but they weren't especially cheap by today's standards, although I bought a FORTRAN compiler for my Cromemco system of lost antiquity for what I considered a fair price. That was in the pre-IBM PC days, however, and the OS was a variant of CP/M.
I think you can find IDE support for FORTRAN as a plugin for Eclipse, although probably it's easier just to edit the source as plain text files in VS. If free is what you need, there's probably a way to run the gcc fortran compiler in a mode that outputs in Windows-linkable form. Speaking of antiquity, it's been a long time since I did Windows binaries, but I believe that what you want is "COFF" form compiler output.
IBM's mainframe FORTRAN required an extensive runtime framework and support libraries. I don't know if the Windows system does or not, or whether you already have those resources.
Depending on the application, it might just be easier to convert the app to run in a Linux environment under cygwin or in a Linux VM. Either that or crack open the piggybank and break out the Intel software catalog.
Customer surveys are for companies who didn't pay proper attention to begin with.