Apparently the distinguishing feature of Frostgrave is that each warband is build around a wizard and an apprentice. So I've started converting leftover miniatures into 17th-century spellcasters.
The generic duo is entirely Warlord Games plastics, except for the greenstuff and red beads. The Scotsmen are also Warlord-based, but with Gripping Beast spear arms and I think one Perry Zouave arm. The Cossack apprentice is a Zouave with a GB spear arm, and the older Cossack is a Fireforge Mongol with Warlord pike arms and a cut-down GW spearhead.