Just found a wonderful blog site: http://regencymusicaltimeline.blogspot.com
It has details of what composers were around during the Regency, and more importantly, what music of theirs was known/popular. Also features brief biographies and descriptions of composers' works.
If I could draw your attention to the Schubert entry - entitled "Appropriate, but out of bounds"... because, as the author notes, most of his work was not published until after the Regency period. Very useful to have a blogger who considers whether a composer's music could 'safely' be referenced in a Regency setting