Yep, most shops that I know of want to use Dot 4, in fact Dot 5.1 is a very strange request. I doubt anyone would offer Dot 5 and if they do, I would be leaving....
Anyway, I always bring my own purchased from a motorbike shop. I think most of them would have it at about $18 per 500ml bottle, which will easily do a flush, including the clutch.
If you need a full change 2 bottles is normally enough.
My brand that I trust is Motul 5.1, which I think used to be called (or still is) EBF600 or something similar.