It is impossible to merge two directories using a single symlink, since a link can only have one target. This applies equally to junctions and symbolic links. (On Linux this could be achieved at VFS layer, by using virtual filesystems such as overlayfs or unionfs; some other Unix-like systems also have similar concepts of "union mounts". No such thing on Windows, unfortunately.)
But if the
.bin file names always stay the same, you can create symlinks to the files directly:
mklink /f c:\bins\001.bin d:\001.bin
mklink /f c:\bins\002.bin d:\002.bin
mklink /f c:\bins\003.bin h:\003.bin
mklink /f c:\bins\004.bin h:\004.bin
...and so on
This could be rewritten as:
for /f %f in (d:\*.bin) do mklink /f "c:\bins\%~nxf" "%~f"
for /f %f in (h:\*.bin) do mklink /f "c:\bins\%~nxf" "%~f"