I have a pink mesh harness I got my moms puppy and it was way too small for her- she was already 6lbs when we got her... never worn/brand new.
I could send it to you if you want just pay for shipping which shouldn't be more than $4.
Four Paws Pink Comfort Control Dog Harness, Medium
It's this one and it's an xs and would definitely fit a 3-4lb dog.