No, no such thing as a 57 Ostvolk, no need for it, there was no swastika on the wartime version, so no need to change it!!
There were Ostvolk's made postwar, and can be found in 57 vets groupings and on medalbars etc.
S&L made them, Souval too, and possibly others!! But they should'nt be called 57ers, however, there is a difference IMO between a piece made, say by S&L in the 1960, and some of the modern stuff found on E-bay!!!