You do not say where you are. But, here in the US just about every hardware store will sell 10 / 3 (10 AWG 3 Conductor cable) and you can then buy the ends and make it yourself.
I believe him because none of those cables are available in my country, even the connectors are not up for the task when powering my power-hungry what miners (15-16amps).
OP you are going to need to buy the cable online, I do have a great source in China but they won't sell small quantities so just get it online if you can.
3 × 2.0 mm² of 20 A that you mention is the recommended
Sorry but recommended by who? The recommended wire size for his 3.3kw load on 220v is 2.5 mm2 60c (at least that's the case in the U.S), Whatsminer, however, will ship their 3.3-3.4kw gears with 2mm2 cables which anyone who follows the code would not use, you will run into an issue with your insurance company if shit hits the fan, also it doesn't have to be 3x, since the ground wire could be made smaller and I have seen such cables many times, searching for 3x something for cables online is usually a bad idea, the correct search term is 19C 2.5mm2 power cord.
So to make a long story short for OP.
The minimum is 2.0mm2 for your load (it will work, won't get hot, and it's ok in some countries, not ok in some).
The Perfect is 2.5mm2((it will work, won't get hot, okay in ALL countries).
Oh, and if you are going to shop on U.S based store, the 2.5mm2 is called 14AWG.