As far as the UK is concerned, between 1919 and 1929, Steinways
(Hamburg) supplied exactly 19 'B' grands in total in elongated cases
to the British Aeolian Company for equipping as Pianola pianos.  This
information comes directly from the original (saved!) Steinway London
sales ledgers.

Most had plain cases, though at least one had an art case.  As usual
they were supplied without legs, lyre and perhaps music desk, which
were furnished by Aeolian.  The player mechanisms are typical Brit
Aeolian, with varying stack sizes and detailing.

The 'O' grand was the size of piano that Duo-Art rolls were conceived
for and edited on (in the UK at least), but the 'B' Duo-Arts can sound
very convincing when correctly set up, with of course a bigger dynamic
range and the signature 'B' sound.

Some seem to have found homes with eminent musicians, such as Sir Henry
Wood.  They must have been very costly, perhaps made only to customers'
order or produced as occasional flagship models by Aeolian.

We know of the existence of, I think, six.  Some are electric-only
Duo-Arts, some are pedal-electric.  One was shipped to the USA.

Some six unsold 'B's, unfinished or gutted, were probably eventually
returned by Aeolian to Steinways and ended up as studio pianos at the
BBC.  I saw one in the 1970s but don't know what has happened to them
since.  This means that there may be perhaps seven lurking in the UK...

The known 'B's change hands infrequently.  I don't know of any for sale
currently, though this correspondence may alter things!

Patrick Handscombe
Wivenhoe, Essex, UK