Beats me why you'd need one for a VGA card though since VGA controllers are (or at least should be) fully backward compatible with EGA and CGA.
As I understand it, the CGA support on VGA cards is "faked". Can't remember for the life of me where I read this; but I do remember that while most CGA displays worked, there were exceptions.
Also, some early games really "hit the hardware", so they actually require CGA emulation to work.
I'm not sure if DosBox covers this or not. I know that M.E.S.S. did, but I also know the PC-XT driver within it hasn't been updated in a long while.
M.E.S.S. (Multi Emulator Super System) is at:
Duffy also has some info and files for setup at:
Click on the "MESS XT Emulation" button.
NOTE: M.E.S.S. XT emulation isn't all that easy to set up.