So other than going to a bar, looks like you either order via cable or online subscription. We're streaming it in our apartment common area using Amazon Fire TV sticks. I did some searching and found at the bottom of this link where you can stream it from.
So we thought we had to stream via Showtime but apparently fire tv doesn't support that? So we are using the UFC tv app which we downloaded to fire tv stick.
There's showtime PPV, UFC.tv, playstation & Sling