There is only one manufacturer of Skydrol fluid. There are many that resell it, and that explains why you see so many Google hits. Also, OEMs advertise that their equipment is compatible with Skydrol, producing many more hits.
and Type V Skydrol fluids can be mixed and used in any proportion, but only on those aircraft for which approval has been granted. Boeing has approved Skydrol 5, and so have Douglas, Gulfstream, Bombardier, and British Aerospace. There are other manufacturers who have evaluated Skydrol 5 and probably would give approval if a customer asked for it.
The current fluids sold are Skydrol LD
-4, Skydrol 500B-4, and Skydrol 5.