Sorry about the black neons. Hope you can find some healthy ones soon.
There's a LFS I go to occasionally but rarely buy from because I so often see them treating their tanks with ich medication. One day when I was in there they had some really nice looking cardinals and I considered buying them. They would sell them, but without their 7 day return guarantee, because they had just recently arrived and were in QT.
Point of the story is - if you take the sick fish, I have no doubt they would tell you that you do so at your own risk and there would be no free ich medication or discount involved :o)
Having said that, however, I have no doubt you could get them healthy because you are such a good fishkeeper.