Have you tried ebay? There are some consistent fabric seller's on there so you can review em before you bid. They might have your tartan. Otherwise, you can look at casual kilt makers' sites, like the sponsors here. I'm sure most if not all sell tartan by the yard. I looked and unfortunately USAkilts doesn't have McNeil of anything, as near as I could tell, but perhaps you'll have more luck with another kilt maker...