It should be possible with a little thought to install an old fixture on to a fan that has been prewired for a light fixture. Home Depot seems to have every part ever invented for light fixtures. You might have to design your own kit. (like mounting a shallow box, or incorporating the existing threaded nipple from the fan fixture)
Also consider installing the fan in the center of the room and adding the older fixture you want to keep to another area in the room. Example might be to install the fan in the center of a bed room and add a box for the other fixture to the front of the door, or over the bed, or ceiling fan in center of kitchen and light over the sink.
Also if you are going to reuse older fixtures, consider replacing the older sockets and wire in the fixture with new wires and ceramic sockets.
If you are just trying to keep an antique globe, these base sizes (4" or 6", etc) have been fairly standard since the invention of lighting, so you may be able to replace the base and reuse the glass.