https://www.torproject.org/docs/bridges

"If you need to get bridges, you can get a bridge by visiting https://bridges.torproject.org/ with your web browser.

You can also get bridges by sending mail to bridges@bridges.torproject.org with the line "get bridges" by itself in the body of the mail. You'll need to send this request from a Gmail, Riseup!, or Yahoo! account, though — we only accept these providers because otherwise we make it too easy for an attacker to make a lot of email addresses and learn about all the bridges...."