Looking for fragrant Oncidium species (butterfly type)

[orchidsarefun]

online is a good suggestion. You should also contact the nurseries and ask them direct.
I haven't come across a really nice scented yellow in my nursery travels. You either get the fragrance or the flower, hardly ever both.
I did see a gomesa at Hausermann's - miniature - but not in flower.....not sure if it was a varicosum which is another spectacular dancing lady type.