I got my duplex lug nuts at discount tire here in town. Any tire/wheel shop SHOULD be able to help you, might also contact the maker of the wheels you are trying to fit.
1)The 1991 Dodge B250, J.Y.D.
2)The 1987 Ford, Wolf-Den
Founder & President of Sooner or Later United Truckers and PROUD TO BE A S.L.U.T. ! !