MAPP, a stabilized mixture of Methylacetylene and Propadiene (and trademark of BOC Gases) yields about 25% more muzzle energy (about 11% more velocity) than Propane.
Available in the plumbing departments of home improvement stores like Home Depot or Lowes.
Your fuel meter would be set up using the same torch head you may have modified for propane, although you'll have to meter in 4.6% by volume instead of the 4.2% of propane.
Keep tank upright to prevent liquid fuel from contacting the torch head. Room temperature tank pressure is 94 psi.
MAPP gas has a noxious rotten egg odor to inform you of the presence of leaks, but you should still use liquid leak detector on all joints.
In Australia it is known as RazorGas and is a trademark of ELGAS. In the UK it is not available to buy, and instead is called MAP pro or MAP plus. It contains propene instead of propadiene and Methylacetylene.