My targets are home-made. I cut a disc out of black poster board: 2", 3", etc. and glue them to a piece of white paper. Then I take them to the print shop and have 100 of each printed on 60 pound white paper. It is remarkably inexpensive.
Commercial targets are printed on a sand coloured paper that takes away from the brightness of the bull, to me anyway, so the black and white contrast works better for me.