If you know someone who can cut out pieces of wood for you, you can make your own dollhouse piano without much effort. It's easy and fun!
Cut two pieces of wood, one for the back, and another thicker curved piece to hammer onto it. (See pictures for one shape idea... you can cut whatever shape you want.) This thicker curved piece makes a spot for the piano players feet, making it look more realistic. (The approximate dimensions for a 1'=1" scale short piano are 3.3" tall x 4.75" long x 1.5" to 2" deep.)
Stain the piano the color you want it. When the stain is completely dry, paste on a keyboard and sheet music.
For a keyboard, do a Google Image Search for "piano keyboard". Print your favorite one, cut, and paste onto your wooden piano. (For a 1'=1" scale, the keyboard should measure .5" wide x 4" long.)
For sheet music, you can either scan in some of your own, or you can do a Google Image Search for "sheet music". Then print, cut and paste onto your piano!
Once everything is completely dry, spray several coats of Clear Acrylic Sealer over it all.