I am on the same quest here as you guys. And i think you guys are looking for springs in the wrong places. Instead of looking for scooter springs why not look for a spring designer company that makes springs. Like this one in Denmark.
I have ordered 4 springs from here and you can read more about it on this forum tread.
These springs comes with compression strength spesification so you can compare numbers against different springs. This makes it easier to find the right one for different setups.
I am not saying that i found the solution, but i found stronger springs that fits in the EU version. I have not been able to test i yet because of the snow and cold weather outside.
Sorry for my bad English language.