The NUS Extra card is now known as TOTUM and you can apply for one at www.totum.com. This card is chargeable and will be posted to you.
You can also join Student Beans (https://ussu.studentbeans.com) or UNiDAYS (https://www.myunidays.com) to obtain similar discounts, both schemes are free to join and are virtual cards/apps that you download to your phone.
The University of Surrey is not a member of the NUS. The decision to leave the NUS was made after an all student referendum in 2017 where the student population voted to leave the NUS.