There used to be an interface for quickly searching available magazines, subscribing, seeing population counts, etc. Does this not exist anymore, or am I just missing it?
Is there some A / B testing going on? I still have Magazines in the top bar. Collections as far as I understood is simply a grouping of various communities & magazines that share the same related topics and I guess setting a collection as favorite will act like you subscribed to them (I haven't really used them before).
Check if any userstyle/userscript is hiding it maybe? It's definitely still there for me, and I'm sure @ernest would have said something if he was A/B testing removing it.
If you have enabled option "Show top bar" then "Magazines" will not be displayed at the top of the page between "People" and "Collections" and you will have to click "All magazines" at the end of top bar to go to the magazine search.