Help Need your help guys

Hi I am new here and I want to ask for your help.

My mom and dad in a vic to the usa, they will be in Washington in10 h and after couple days in new york.

I want to tell them to buy for me asmart phone and I want or mi6 or oneplus 5 idont care which one.

Ineed to tell them where they can buy it with cash not online, and idont know, iwiil love if someone could help me and tell me name of good store the I can trust to point them, its need to be Unlocked

Srry for writing to much but they have only 6 days and they return and I need A phone !

Thank you guys