This is what I found in my cardboard box; a list of retailers for TI-99/4A and its equipment, originally from TI Germany. I seem to remember I actually asked for that list back in those days.
(The addresses are certainly outdated, the ZIP codes are still the old 4-digit ones, and dealers may have long closed their shop and left the market.)
I was living in the Frankfurt area, so I had some choices indeed. Maybe some of the other German users here remember their favorite TI retailer.