I used 16-2 wire to rewire my foot controller on my Singer 15-91. I just went to Home Depot and bought extension cords and cut off the ends. I couldn't find bulk wiring unless I bought a huge 100 foot roll. I paid less than $8 for a 15 foot cord. Under the Vintage Machines tutorials Billy recommended the 16-2.
Maintaining the integrity:
http://www.quiltingboard.com/t-45814-1.htm
I think the original post about 16-2 is somewhere in here:
http://www.quiltingboard.com/t-43881-1.htm