Merrimack, NH
Pinball Resource is your best source but I second Mikala's comment - many times it's not the springs but actually the stepper parts that are the issue. Before buying new springs I would recommend taking apart and cleaning the steppers, then adding a lubricant (very thin coating of it) to the axles, and re-assembling them. I had an issue much like what you are talking about on the ball count stepper of a 1966 Kicker. It could count up but was having trouble re-setting. It would slowly go back. When I took it apart, the axle for the cogs was covered in grease and filth so it was making it stick. After a good cleaning, it went back to working like new.
If you decide to go down this route, take lots of photos of the counters as you take them apart. It can make re-assembly easier.
I added a few photos of the process I went through. I was having trouble with the counter in the upper right of the first photo. I stripped all the mechanical parts of it. The axle I'm holding in the last photo was covered in a black sticky grease (even the cogs) which was making everything move like molasses.
_15_counter (resized).jpg_17_counter (resized).jpg_18_counter (resized).jpg_19_counter (resized).jpg
