Since, you are on 64 bit windows 10.
You might try https://sourceforge.net/projects/mingw-w64/files/Multilib%20Toolchains%28Targetting%20Win32%20and%20Win64%29/ (https://sourceforge.net/projects/mingw-w64/files/Multilib%20Toolchains%28Targetting%20Win32%20and%20Win64%29/)
I have no idea if the installer has FORTRAN.
Edit2: I had installed mingw64 GCC 5.3.0 into i686-5.3.0-win32-sjlj-rt_v4-rev0 and it has gfortran exe in the bin folder.
x86_64-posix-sjlj
x86_64-posix-seh
x86_64-win32-sjlj
x86_64-win32-seh
i686-posix-sjlj
i686-posix-dwarf
i686-win32-sjlj
i686-win32-dwarf
posix/win32 is thread support.
dwarf/sjlj/seh is exception support.
Tim S.