how can i search someone's shop when it's not posted in their profile?

I haven't figured out a way.

If you know of something rare in their shop, you could search for that item and hope it comes up in the search results.

There is no longer any way to search for shop name.

Another thing you might try, but its a long shot. If your browser has the option to view a page without formatting (in firefox, its View, Page Style, No style) you might be able to find a shop link there.