Nearly all the 1998 190s out there will have the foiled rudder and the fourth skeg. The hydrorails were standard equipment in 1999 and were made available as add-ons to the 1998 190s. I know Farmer Ted had his added after the fact, but that was not recent.
My understanding is that the hydrorails had nothing to do with handling characteristics. Their function was to soften the wake a bit. Farmer Ted could certainly give you a good idea about the before and after results of the hydrorails.
I would suggest calling Rambo Marine, Charlotte Ski Boats, and Bay Area Water Sports. Any of those dealers could have some lying around or could give you a reasonable idea on the likelihood of your finding some.
Previous: 1993 Prostar 205
Red 1998 Closed Bow Ski Boat, PCM GT40, 310 hp, Standard Gear Reduction, Acme 4 blade, Perfect Pass SG/Zbox.
Tyler Ski Club
Be kind. Have fun.