Not yet.
I spent the day on the Clee Hills, Shropshire, looking for stones. Zillions , but few quite big enough and mostly rectangular. There's a quarry there, and I tracked down a digger driver in the pub! He says they put the big ones, maybe 10 tons, on one side to crush separately so I'll try to see the manager on Monday (though oblong is rare he says).

I did find a concrete block, about 11ft 6 in x 2ft 6 in x 3 ft (four or five tons?), the remains of old mining buildings. perched high up with a fabulous view. Tons of room to practise, and it would look good temporarily erected if we wanted to. I'll send a pic through stonehengeneers if it's likely to be of interest.