Stefan,
Even though it was sold, the KOTCS Repo Rucksack is still posted in the Cairo Bazaar. COW member RaiderZee was the seller. You may want to contact him directly.
I got my repro rucksack through CFI Military on eBay.UK; this model is no longer listed, so he's either temporarily or permanently out of them.
If you do an internet search for "Gebirgsrucksack oliv gepolst", you will find several German vendors of this bag, still in stock. Make sure they can sell/ship to your country.
And make sure to search for the OLD version of the "Gebirgs-" / "Gebirgsjägerrucksack", since the newer version has plastic buckles.
You should also be aware that the material of the straps (pleather, no real leather) and the overall quality of the repros is much lower than you would expect it from the original military product.