These two units are a kind of "build them and they will field them." Sadly my confidence that Byzantine army lists were bound to have Light Infantry armed with javelins seems to be misplaced. The best I could find were the Manichei in the Comnenan list, so ferocious heretic Slavs they will have to be. Whether they look the part or not I have no idea, but I can claim they have been equipped from Byzantine military stores.
They are actually the remnants of the pack of Old Glory Byzantine light infantry (skirmishers) I purchased earlier this year along with a pack of spearmen. All done now, so that is good news.