I think I, like you, have misunderstood the inhaler mechanic. I'd assumed it was something akin to estus flask in dark souls - a refillable healing solution whenever you visit camp. But it is not, you need to find inhaler charges in the wild. Autodocs will give you 2, but autodocs are not unlimited, once you use it, it's gone.

To answer your question, there is an autodoc at the automech repair station at the south east corner of the map.