The adjective clause in the new sentence follows very much the same pattern as the adjective clause in the sample sentence.
The thing with a clause is, it must be complete. You can see where that clause begins, right? Are you having trouble seeing where it ends?
There once was a place / where . . .
What follows is going to describe "place," so it's going to be adjectival. It begins with "where," so we know it will be a clause. (And not just a phrase.)
Clauses have their own subjects and predicates. So you have to look for a group of words that goes together and that has both a subject and a predicate.
There once was a place / where you could get [subject and verb, but the verb is left hanging]
There once was a place / where you could get whatever [subject and verb and the start of the thing that gets the action of the verb]
There once was a place / where you could get whatever you needed [subject and verb and the complete thing that gets the action of the verb, also know as a direct object]