Manifold Vacuum Experiment

Anyone got any good sources for low vac canisters that add ~20deg or so?
I bought an accel one because the manual showed a graph with a low all-in vacuum, but when I tested it with a hand pump, the all in is like 16" and I'm looking for 7-10".
The low vac corvette one everyone used to use on bullet distributors are NLA, as far as my searching has yielded. Got skunked on ebay too.