I have found 2 springs that looks to be very similar to my spring.
You can see here that there is also stronger springs that will fit our pulley here:
Taken from here page 201:
As you see I have compared the springs with my numbers at bottom of picture.
I am not sure about how heavy weights you guys are running with. But my experience is that more strenght on the rear spring heavier weights are needed.
So for you guys that have more power than me and wants to experience with stronger springs. You also need to buy heavier weights. 7,8,9 or even 10 grams per roller. Could be more, but just be prepared.
Hopes this helps you guys!!