White is not a dilution gene; chances are that it will severly mess up buff colouration and likely add pattern/smut to the plumage. Black or blue would be a better choice--at least you will know WHAT you are adding--white is an OFFSWITCH that turns OFF any colour or pattern genes present in the bird. Since they are turned OFF, you do not know that they are or are not present and cannot select for or against them. Thus, every white is genetically different except for carryong two copies of recessive white.
Have you checked eggbid or any of the silkie yahoo groups (and I think there may be a showgirl yahoo group, too) to find a buff showgirl breeder?