You can still buy Ambroid if you look hard enough, but it seems to be available only in the small tubes. And the price seems to be about the same even though you are only getting about half the glue in the small tubes.
I've been ordering Sigment straight from Sig. It's OK, but somehow I still like the Ambroid because it's a thinner viscosity.
Lou Proctor aways recommended Duco Cement. He was a master craftsman and told me once that Duco was the strongest of all the cements. It smells funny to me, but seems to work about the same as Ambroid. Duco also comes in smaller tubes, and is pretty expensive if you buy it at the local hardware store.
I visited the Proctor Enterprises business in Sandy, Oregon just last week. They still sell Duco, and the price struck me as much cheaper than at my local Ace Hardware. I think the price at Proctor was about $2.50 per tube.
Dick