The best known work for harmonium and piano is the "Petite Messe solenelle" by Rossini. But it is only one of many compositions in which an antique harmonium from the composer's time is used. It is owed to the composer to interpret this work with a Debain harmonium.
I've heard of performances that even used a suction wind harmonium. Or a keyboard. A shame!
But - it's not that easy to play a harmonium. And especially if you have never played on it. You can't just sit down at a harmonium as a pianist or organist and start playing. This is sure to go wrong! Especially the expressive playing requires a lot of knowledge of the harmonium playing and also a good knowledge of the respective instrument.
With me you can choose between 2 historical Debain harmoniums for hire and, if necessary, book me as a harmonist.
Your audience will thank you when you hear this wonderful mass on a Debain from Rossini's time and possibly from an experienced harmonium player.