Source for 150mm Brake shoes?

My 301 has standard cast alloy wheels, I've had to shim out the brake actuator inside the drum as my brake shoes are worn right down and I needed to pass the MOT.
Now that I've come to look for replacement shoes, all I can find is 140mm and 160mm.
Does anyone know where I can get some? or do I just get my old one's re-done?
I prefer to have decent rear brakes as I frequently pull a trailer with my bike.
Cheers, Dave.
Now that I've come to look for replacement shoes, all I can find is 140mm and 160mm.
Does anyone know where I can get some? or do I just get my old one's re-done?
I prefer to have decent rear brakes as I frequently pull a trailer with my bike.
Cheers, Dave.