The classic exposed core strings were Superwound. They seemed to be part of Rotosound with the same address in England and everything but was always marketed as if it were a different company (Toyota vs. Lexus? Makes no sense to me).
They were unavailable for many years, but these days Rotosound sells them as PSD (Piano String Design, which was what Superwound called them, but don't get me started again). Back in the old days, there were a number of different models for different basses, since the distance between the bridge pieces and the ball position varies from bass to bass. These days, they sell one model with an adjustable ball end which you can set for your instrument.
The Superwounds were my favorite strings for many years, especially on the original L-2 Steinberger (this was the OEM string for the early ones).
As mentioned above, using them on an Alembic is problematic since you can't individually adjust bridge height.
David Fung