You could use this cable assembly, but I don't know if it would fit your brake lever. You never addressed if you had a lever or not, and what diameter the hole is for the cable. The item below would work "most likely" noting that I have not measured your brake drum, or anything else. There is a Rupp brake lever assy available from OldMiniBikes that would fit this, but it's not correct for your bike.
165-005 Baja OEM Brake Cable
Or, you could get this lever and cable kit:
7/8" Brake Lever & Cable (NOS)
You'd also need this step retainer that goes though the cable hole on your brake drum assembly, noting again, you did not provide the diameter of the hole:
Step Retainer - AZ2373
You'd need two of these jam nuts for the step retainer above:
1/4-28 - Jam Nut - AZ8531 Fine thread
And a spring like this that goes between your step retainer and your brake arm, so the brake and cable will spring back (release) when you release the brake lever.
.438"OD 5/16"ID 3-1/8" Length Spring azusa 2390 az2390
This piece is to clamp the end of the cable as it exits your brake arm.
Cable Control Fitting - AZ2360
This is the best I can do without knowing anything about your bike, not seeing it, and not measuring it.