I confess myself baffled by onion powder. It seems that almost every American recipe uses it (slight exaggeration!) Same with garlic powder. I'm sure it is available in Europe, but have never seen it in the stores or seen anyone use it. If we want onions, we use onions. If we want garlic, we use garlic.
What is the explanation? Don't you have access to real onions and garlic?
Onion Powder
Thinking about this odd culinary phenonemon, I went looking for onion powder in China. It is available. In 100 cwt sacks for industrial usage. It is also available in more sensibly sized containers for use in the domestic kitchen - but only from expensive import stores. (Even though it was probably produced in China, in the first place.)
The only thing I do come across other than fresh onions (in many forms) and garlic is this dried wild onion, although I've no idea what people do with it. I have asked friends, but just get blank looks.
Most mysterious.