Technically he is right. but everyone understands what you mean so hes just being too precise.
A correct way would be: The Walmart i usually go to...

Its not plural because they decided to name the town Two Egg.
Depending on the kind of shop you could do some word play with the Egg being plural. But if you just want the name of the town then Two Egg would be correct.

I find a pet store that sells ferrets is wrong.
I found(past tense) a pet store that sells ferrets is right.
Sold only if they used to sell them but they do not sell them anymore.

Let his come in is wrong.
Let his cat come in is right.
If the cat is a he then let him come in is also right. (him referring to the cat)