Newb-question - Kratky-method

So i am new to this and would like to try the kratky method for a start.

But i already ran into a wall: What Fertilizer should i buy.

All my local garden centers sell guano, literally shit, and there are so many different bottles that my head hurts if i only think about it. And the Hydroponic Fertilizers i can find on Amazon.de are all fairly low on NPK percentages.

I would love to buy some Masterblend 20-18-38, but they don't send to my country.

What to do ?