Have you thought of doing a bit of googling. I am sure there are websites with old versions of the internet floating around. You might be able to use some sort of "Way back machine" to see your stuff again?
Welcome back. Good to see you!
You asked the same question in 2020 https://www.diygokarts.com/community/threads/pictures.44715/#post-559733
I dont think albums were pulled over in the change of forum software. Looking at AI's response below, I think all your pictures probably werent imported...
Maybe you can contact some of the US manufacturers and explain your situation. They could maybe suggest some cheaper alternatives in the Netherlands. Or they might be able to tell what other engine springs might fit that are more available where you are
I look forward to seeing how this projects progresses. Have you tried Arc Racing for parts? They might have springs that will fit and that are stiffer that stock.
Ugh....I just saw that you are in the Netherlands. I am not too sure where you might get any parts there. Shipping is always going...
https://www.gopowersports.com/ is just one of the online places you can get kart related stuff from. Bearings, nuts, etc can be bought at your general hardware store type place