Are you talking about the toxic waste sweet, if you are I don't even think they are sour. They need to make a more sour lime, it gets boring eating them now lol.
I haven't found anything yet that I think is really sour.
I'd say impossible. But I did found an online store, which sells all sort of Finnish stuff for people living abroad. Here is their salmiac section. I'd say the prices are reasonable compared to prices here. That salmiac chocolate is some interesting stuff too.
How cool that you can order all this good stuff from home where ever you are.
I done that in college, they are pretty sour but i've tasted this chewy stuff with powder inside and it literally made my eyes water.... don't know the name though.