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 many are willing to interchange. Hopwever, tango music is seldom performed in the same fashion, it is nearly a must that a tango ensemble develop a style and hence use own arrangements using the basic published material.
But there are also services to for writing arrangements you may order.
Below you will find a compilation of some commercial available pieces. If the publisher is known, it should be more probable to get it from a music store or directly from the publisher. For addresses see the list of tango publishers.