Here's my take/experience wit this.... even if you get a fairly modern (9speed era) Shimano mtb FD that will handle a 48t
big ring, you'll still run into problems b/c the cage is stepped and it wants a 12t gap between the big'n'middle, and
a 10t gap between middle'n'little. You can make it work, but it will be sloppy, b/c they essentially optimized the geo f or
their own Shimano-branded 48/36/26 cranks.
Best bet, as others stated, would be to get an 80s/early 90s mtb FD. Most will take a 48t top, and lack the radical steps
in the cage that demand specific tooth counts. I have an early 90s Suntour XC Expert that came on a microdrive bike, but handles
a 48t top, plus most of the various deerhead/mt60/exage FDs I've come across take a 48t top as well. These are easily sourced, and most often do not cost much....
IME, the 6- and 7-speed FD's handle wider chain better than the 9- and 10-speed ones do.... less rub and whatnot.
Good luck!