There may still be a bit of old stuff going spare down on Avonmouth. I don't think they've cleared the site yet, but would need to check.
If you want concrete, we've got a couple of manhole rings out the back at work (near M5 J17) that are left over from before we sold off our contracting arm. From memory, they are 2.4m diameter and 1.5m tall. I did enquire about these before, but the boss hasn't got around to thinking about it yet. If they were definitely wanted, I could pick it up again and try to sort a deal. You'd obviously need to sort transport, but we may have a machine available to load them; again, I'd need to check, but best to be sure they are wanted before trying to sort anything.