I used a set of springs that fit an older Harley FX , XL and XLCH. that used a Showa 35 mm fork. The springs are A bit longerthe wire they are wound of heavier. I have the specs some where.
Being longer and thicker wire they are much stronger.
With the adjustable caps, in the softest setting, on the later forks I get about 25 mm sag. The stock springs were closer to 40 mm.
On the second setting it's about 12 mm sag.
I got them from J&P, item # 230-584, $49.99 a set when I bought them, last I checked they are $49.99.
With the Minton Mods on the dampers and about 7.5 ounces of ATF they work very well.
Leo