While I don't know where to specifically go shopping, there is a difference between a ukulele and the instruments you may be looking for.
The ukulele is not a Portuguese made guitar. It was developed in Hawaii. It is based on the Portuguese Machete, Braguinha and Cabaquhno. (These instruments are similar but originally came from different parts of Portugal and mostly from the Canary Islands.)
If you want a Portuguese guitar, it would be best to not ask for a ukulele. They are different instruments. If you insist on asking for a ukulele, you will probably get something made in Asia or the U.S.
By the way, the Portuguese word for ukulele is......ukulele.
I dabble in the ukulele which is why I know this.