Follow the directions to Li Mizzani, but at the fork in the road where you turn left for that now signposted site, go right following signs to a church instead. Keep going, not far past the path to the church and 2.2km from the turn, you'll find an old wooden ladder and a more modern white metal one to help you climb over the dry stone wall under a tree on the right, with a fallen info board.
There's more than a tomba here!
A fallen menhir, the remains of a round building and a more recent rectangular building too.
The tomba itself ... sadly ruinous; there's no stele, no funeral corridor, all that remains is the esedra and that's quite overgrown. You could almost miss it while standing in front of it.
One for completists - we'd driven part way down the road 18 months before and not found this site, so I'd been determined to see what was there ....