Hi Pianoman,
to the data:
it should be this one:
Fantaisie & fugue pour le piano : pour la main droite seule ; op. 41
Auguste Dupont
15 pages
Bruxelles [u.a.] : Schott [ca. 1879]
It's in some libraries ( Switzerland: RERO-catalog / Cantonale Library Lausanne. Austria: Library of the Universität für Musik und darstellende Kunst Wien. Germany: Dresden SLUB.
Great Britain: Univ. of Cambridge Library + British Library.)
I checked some catalogues in the web, too, but without success. And it's not on the actual Schott-page / catalog.
But perhaps there are antique bookstores (web), which I haven't checked, or one could ask Schott directly for the old stuff, or somebody else here has got it.
Cordially, 8_octaves!