Big & Tall Adoption Agency is an adoption center featured in Sam & Cat. It is a place to adopt "plus sized" kids. Goomer was adopted here.
This is the first location outside of California to be mentioned by name (Seattle doesn't count as it's a city).
You apparently get receipts for the children adopted as Mrs. Merr said when she adopted Gieux Merr she should've kept the receipt. Although that could've just been just used as an insult to how disgusted she was at him.
It is most likely located in Louisiana as that is where Mrs. Merr and Goomer lived.