You can have pipe custom rolled to any diameter, any reasonably thickness. If it is short sections, you are essentially buy a vessel. If there is miles of it, there are pipe companies that specialize in that kind of fabrication. AWWA has a number of standards on water piping that may apply. Search for "penstocks" as another term, also.
What kind of help are you looking for? Suppliers? Dimensions? (Ask the suppliers!)