Yeah same, I've tried finding them in local stores a long while ago and all of them basically looked at me like I'm asking for a moon rock or something.
where do you live? At least here in germany there are some sites selling B- and I- Type (Bosch/Item) compatible aluminium profiles for ~15eur/m with custom lengths (the heavy duty B-Type 45x45) I personally build most of the stuff out of these profiles, easy, sturdy and reusable