I finally found what I was looking for at the Istanbul Spice Bazaar (Misir Çarsisi): mint crystals.
For the Nokians and other Finnish sauna freaks reading this, this is the stuff that you want to mix with a little bit of water (else your sauna is way to dry, of course) and then put the mixture on the hot stones. Crystalised mint is a very pure form of mint. Mint in a sauna gives a very cold and cool feeling on your body. Meanwhile your sauna is obviously very hot. You basically think that it’s cold, yet it’s very hot.
Well, with crystlized mint you maximize this. Eucalyptus is nothing compared to mint crystals. Chinese mint comes close, though. But not quite.
The aftermath is that you probably don’t want to jump in ice water after your sauna anymore. Not before adapting to normal temperatures for ten minutes. You wouldn’t be the first who passes out. I mean, your body is in a very confused state: it behaves as if it’s cold, but it sweats as if it’s very hot. The one thing you don’t want to do is to make it very cold suddenly. Unless you are a big dangerous looking Finnish dude, maybe.
I mean, I’m not underestimating the Finnish sauna people. I’ve been to a public one in Helsinki. Woah.
Anyway. The store can send the crystals to your home with DHL, the owner told me.
If any of the Nokians or other Finnish sauna pussies want to know what a real sauna experience is, you can mail them at ucuzcular@gmail.com, and try it.