Water pumps for all model Fieros are readily available at parts stores. The water pump in the V-6 should NOT be replaced with a pump having a plastic impeller. If the engine overheats, the plastic impeller will spin on its shaft and thereafter fail to pump sufficient coolant. This leads to chronic overheating and possible damage. Replacement pumps should have metal impellers only. Metal impellers should also be the "closed" type such that you can see the vanes only from the side. It will look much like a vented brake rotor.
Replacement pumps which have worked well in the V6 are TRW/Carter PN# FP1843 and Pronto WP 281 (may be labeled Part # 18-205 or WP-561). You can see the vanes in these pumps only from the side. The impeller should not be the "open" type where you can see exposed vanes. Whatever pump you choose, be certain to verify the impeller is metal.