I think what I'm asking about are over shot wads rather than over powder wads - that is, the hard carboard-like wads rather than vegetable fiber or felt wads. While vegetable fiber wads can be bought from Walters in just about any diameter wanted, the only thick card-like wads I'm aware of are for shotguns.
Where can wads of the type I seek be obtained between .54 and .55 inch in diameter?