Greene, the Great Purple Hairstreak does indeed use mistletoe and rarely strays from the plants. I have only seen the butterfly once in eight years of doing this and that was at a plant nursery that backs up to some woods. BAMONA has a good fact sheet on the Great Purple Hairstreak and indicates that it uses Phoradendron species of Mistletoe:
http://www.butterfliesandmoths... It's also a more widespread butterfly than I originally thought; check the sightings map on the BAMONA page.
If you want mistletoe, I'd say the easiest thing to do would be to find some growing (usually in oak trees around these parts) and ask the landowner if you can have some. Although, I don't know if they can be grown from cuttings or not. Unfortunately, they're kind of hard to spot right now. When the trees lost their leaves a few months ago I saw some clumps of mistletoe, but they're much harder to find when the tree has leafed out. Greene, the link you posted mentions that fact. Also, Mistletoe is considered a parasite although I don't think it ever gets aggressive enough to kill trees. I've never heard of that happening, anyway. And if you have pets or children, be aware it is toxic, as are many host plants for butterflies.
