A different story is finding sheet music for the bandoneon.
Printed scored for bandoneon are quite seldom because of no
commercial interest by the involved editors. The other reason is, that
the bandoneon was always onsidered not to be a serious instrument
so composers preferred to publish their creations as piano scores.
As a consequence bandoneonists are used to make their own arrangements
transscribing the available piano notes. The few ever published in Argentina
or elsewhere where thought mainly for students and are nowadays hard
to find as originals.
Here you can find the list of bandoneon solos
registered at SADAIC
(Sociedad Argentina de Autores y Compositores de Música).
Most solos for bandoneon are arranged individually, that is,
they are not published. As a consequence photocopies of such
arrangements are circulating among the musicians.
More often there are excerpts for the bandoneon as part of
orchestration arrangements. Again, complete orchestration
arrangents are now available at the publisher's on-line services.
Fortunately today's bandoneonists do have consistently
solid knowledge of music. This favors the creation of arrangements,
and many share them with their pupils.
As already mentioned, the arrangement of the instrumentation is part of the
identity of the orchestra and written individually based on the commercially
available basic published material.