Hey Microbus,
I found some piping:
Got it free as well and it includes end stops.
Basically its 6 inch diameter water main (which also means its extremely strong - 1/2 inch thick walls). You can literally jump up and down on it and it doesn't bend.
I got it off some workmen who were installing a new water main near my home. I just asked if they had an offcut, they didn't but were going to cut the pipe anyway so they cut me a length. The end stops are used once then thrown away (looks like they were going to bury them in the hole!) so I asked for those as well.
Guess you just need to find some workmen now!!!
Al.