Step, if you ever read the disclaimer in the mico-brake lock box, you might note that they specifically say not to use the mico lock for extended parking or as a replacement for parking brakes.
Your suggestion about finding a local source for cables is a good Idea, I used to get cables made from the place that made our more custom hoses, but in part that was because they also did a lot of marine business and had customers needing custom made cables for boat motor steering and controls. Maybe some marina stores might know who could make up the cable for the OP.