Rock Auto has the seal or a complete rebuild kit.

GATES Part # 348710 Power Steering Repair Kit
W/Chrysler P.S. Pump

GATES Part # 351170 More Information About this Part Power Steering Repair Kit
W/Chrysler P.S. Pump

BE SURE you have the correct pulley puller. You cannot replace the seal without it. It is not keyed on and held on with a nut like the Saginaw pump, it is pressed on. The puller wraps around that big flange and then presses the pulley off the shaft.
If you do decide to get a new pump you MUST remove your old pulley before using your old pump as a core - you will NOT get the pulley with a rebuilt pump!

Be SURE you mean the Federal pump, NOT the TRW pump. They look nearly identical but I have never rebuilt a TRW pump, so I can't say if they are the same. TRW pumps came on some 68 and back big block motors. A TRW pump pulley presses on also.