Well I suppose it depends on your price range and what not but here's a page from the vocaloid wiki's recommended sites for cosplay
link If your looking for a wig I recommend Arda Wigs they're actually based in Chicago so unlike most Cosplay websites you won't be waiting over a mês for your order and they have really good customer service :)
link as a note on wigs if your buying one to look like Miku, make sure you get twin tail extensions and not just a long wig to put into twin tails yourself. Hope this helps!
