not entirely unpublished; Hadley published an
Annie Polka with Ditson in 1884 - see
here for at least a partial online scan. the site also has a
Clara mazurka Ditson published the next year. They are, mind, piano/piano4h versions. so i find myself mistaken since you did say
orchestral dance music- though the site does have those, in parts - i think rarely score also - for some other composers.
note in passing- LoC American Memory site from which those two are selected, has a huge trove of music - not at all entirely by American composers; e.g. the first edition of Schumann's op118 kindersonaten is there - by American/US publishers over a certain time period scanned. not very well-scanned, I think- lots of deskewing and cropping needs to be done to get it to look nice - but the service is by me very very much appreciated, i at least will say...