There should be an ID tag on the side. The first 2 numbers indicate the distributor series.
Mine is a 23 series I bought in 2000. There are two mechanical advance types, YL or YT, but I can't remember which mine is.
For mine, the cap part number is 270, and the rotor part number is 309. I never had any problems finding them in normal auto parts stores.
Googling should produce sources too.
I don't know if it still works, but the Mallory tech line I called in 2000 was 216-388-8300 x500.
Side notes:
They may have long since solved their problems, but back then they had miserable condensers (capacitors) that failed regularly - after several strandings at the side of the road and hot calls to the tech line, someone finally suggested I get any old Chev condenser since Mallory was having "supplier problems." I did, and never had another problem.
Also, after about 10 years of running the dual points, I bought a Pertronics unit for it and have no points or capacitor now.
Hope this helps.
Dave