I need to find chemicals for developers [home brew]
Ok, that's more specific.
Camera stores are not the place to look for this; they don't support homebrew anything. There are many threads on how to obtain chemistry for DIY developers etc. My advice is always to shop around based on what you need, as one-stop-shopping is usually not feasible or not attractive economically. Also, forget about trying to source everything in physical stores; it's not going to work, period.
For the photography-specific chemicals like hydroquinone, phenidone, etc., try Fototechnik Suvatlar (price list & contact through this link:
https://www.moersch-photochemie.de/en/rohchemie/) or use eBay to search for what you need and have it shipped to you from e.g. Italy.
Chemistry that's not specifically photo-related but still not of the supermarket variety, use something like eBay etc. Think of stuff like potassium bromide etc. You can also use dedicated online stores for raw chemistry; I don't know the ones to use in Germany; you'll have to shop around a bit and/or use AI to find sources.
Finally there's chemistry of the 'supermarket' variety which can be had in normal shops. Think of sodium carbonate which is mostly sold in supermarket, sodium hydroxide that's generally available in hardware stores as pellets for unclogging drains, acetic acid which is sold for cleaning (unscented cleaning vinegar), sodium thiosulfate which is sold in hardware stores and pool supply stores for dechlorination of swimming pools and vitamin C (ascorbic acid) and citric acid which are available in drugstores as a food supplement.
So, in short, shop around based on the specific ingredients you need. Don't expect one-stop-shop, and forget about walking into a physical shop and finding everything.