a butter stick is 1/4 lb
try this: http://www.ebay.com/itm/Vintage-Tupperware-Harvest-Gold-1-4-lb-1-stick-covered-butter-dish-EUC-/251385151522
1/4 lb (1 stick) butter mold. Price: $4.99 plus S&H (I would recommend this one, because it makes a perfect stick of butter.)
or this...