A different story is finding sheet music for the bandoneon. Fortunately today's bandoneonists do have regularly a solid knowledge of music. This favors the creation of arrangements, and which find their way among musicians in form of copies. Anyway, tango music is seldom performed in the same fashion, it is nearly a must that a tango ensemble play a characteristic style and hence require the stylistic adaption starting from the basic material.
Perhaps you are not familiar with writing arrangements and you want order arrangements.
Below you will find a compilation of some commercial available pieces. If the publisher is known, it should be more probable to gat it from a music store or directly from the publisher. For addresses see the list of tango publishers.
Here you can find the list of bandoneon solos
(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.