Luigi70 after creating hundreds of cars for F1 Challenge, is porting over all his work to rF1 and all the cars are ingame. There's a bit of everything, from '50s to '70s and some prewar '20s and '30s in his pipeline aswell (or at least, I remember seeing some of those models for F1 Challenge). But '55 is definitely at the top of his list.
The team I was part of (CROMS, now named OMS or something like that) that made the '65 mod is currently working on a scratch made '58 mod aswell.
Then there is a scratch made (?) '49 Talbot for GTA San Andreas ( http://www.gtainside.com/en/sanandre...bot-lago-t26c/
) that could be converted aswell, and I've seen few models that were going to be added to the '37 mod such as the conversions from the dead game SRW, an Alfa Romeo 2300 converted from somewhere else and a Fiat Mefistotele (which is also known as the Beast of Turin) and that's pretty much it, but they all pretty much disappeared so God knows where they are or if they'll ever be released.
The old game "The Saboteur" had a lot of '30s and '40s race cars (which were badge-less, but clearly Alfas, Ferraris, Talbots, Mercedeses and the like, both in GP and sportscar form) aswell, which could be converted as both the game and the studio that developed it simply shut down, but again, nobody cares so nobody works on them.
As the "original" '55 is officially dead as confirmed above by its own author, these are all the -possible- alternatives you have.