Right now there's no online database for
hoards or
Byzantine coin finds in general. I'm involved in a project directed by
Princeton and we
hope to have a significant database available for the public in the near future.
http://coinage.princeton.edu/In the meantime you can use the following works covering the early
Byzantine period:
C.
MORRISSON, V. POPOVIĆ & V. IVANIŠEVIĆ, eds., Les tré
sors monétaires byzantins
des Balkans et d'Asie Mineure (491-713),
Paris, 2006.
H.-C.
NOESKE, Münzfunde aus Ägypten I. Die Münzfunde
des ägyptischen Pilgerzentrums Abu Mina und die Vergleichsfunde aus den Diocesen Aegyptus und
Oriens vom 4.-8. Jh. n. Chr.,
Berlin, 2000.
G.
BIJOVSKY, Gold coin and small change: monetary circulation in fifth-seventh century
Byzantine Palestine, Trieste, 2012.
E.
ARSLAN (ed.), Repertorio dei ritrovamenti di
moneta Altomedievale in
Italia (489-1002).
http://www.ermannoarslan.it/Repertorio/index.php