For those of you looking for foam brushes without the plastic insert, True Value seems to carry them. I believe True Value stores are each independently owned franchises so this may not apply everywhere, but the several I've been to in the DC-MD-VA area all carry the brushes with a full wood handle.
I've been able to get them at Viking in Maine. More info in the comments under the "Finding varnishing rather challenging" post. Those brushes made a huge difference for me.