I just had a set relined by a motor factors. Not for an enfield but they were on another bike which had truly apalling brakes.
I was a bit put off by the price but having ridden the bike, I'm going to get my bullets ones done too with the same stuff.
For reference they used TRIMAC MR2215 on mine. I think that's a UK company but I'm sure there is a US equivalent. Ferrodo always used to be the goto relining material.
The motor factors I used usually deals with heavy goods vehicles but they said they can get pretty much anything relined. I did have to shape them a little with some course zinc oxide paper and put a chamfer on the leading edge but they were pretty close to concentric out of the box, just a little over-thick, I didn't need to mess about with chalk lines and suchlike.
EDIT: I should add, there is a lot you can do with setup on bullet brakes, a small tweak can be the difference between adequate and apalling brakes. Particularly getting the shoes centred and paralell with the drum. I tend to do the final tightening of either the hub centre nut on the front or the wheel spindle and anti-torque bolt on the rear with the wheel in place and the brake held on so everything is centred before being locked-down.