You can't buy it from TM directly. They don't send SIMs outside country.
These are great questions valeriarodriguez - thank you for asking, and congratulations on your upcoming trip! Kudos to you for planning in advance.
Customers can pre-purchase the Tourist Plan SIM kit online or over the phone, but both the credit/debit card billing address and the SIM's shipping address are restricted to US addresses. Your plan of having the SIM kit shipped to a friend in the US and using a prepaid US Mastercard or US Visa gift card to use online or during your call to pay are perfectly reasonable. You will need to call our Prepaid team or stop by a store to activate it once you arrive. Please let me know if you have any other questions, we're happy to help you prep for travel!
I will travel to the United States next month. Can I purchase the Tour Kit directly from a T-Mobile store?
Will be charged extra 10$ for a sim starter kit?
Welcome, Mariane, and congrats on the upcoming trip! You can purchase the Tourist Kit at a store, and the $30 (before taxes) includes the SIM starter kit. You can find some more details about the Tourist plan here and here, and take a look here to find a store near your travel destination: store locator.
Wishing you super safe and peaceful travel!