(because as you know, unless there's a secret medieval world war that nobody knows about yet, there would rarely be a chance of finding battles where the Flemish and English fought against the Germans and Italians).
Neuss 1474-1475 would come pretty close by giving you a chance to pit a Burgundian army (featuring Flemish levies as well as English and Italian mercenaries) against Germans. The historical field actions were relatively small, but there was potential for a full scale clash.
As for building Italian swordsmen, the swords in the Agincourt sets are quite nice, but the arms wielding them might not be the most Italian looking ones out there - though you could always cut them off at the wrist and glue the hands to other arms. Alternatively, Perrys do produce some pretty decent looking metal Italian swordsmen. As for spearmen, could shortening the plastic pikes give something reasonable looking?