Bernina Express bus from Lugano to Tirano has only 1 seat available, I need 2!

I agree that it's very odd for the bus to be nearly full so early. Perhaps that's an error.

Please clarify your schedule. Are you trying to wake up in Lugano the day of your Bernina Express trip? If so, what time does your train leave?

I don't think there's any public-transit option that will be as fast as a direct bus, but it will be possible to get to Tirano. The issue is the timing. You might need to go a day earlier and spend the night in Tirano.

I think one possibility (though I know nothing about frequency) would be a bus from Lugano across the border to Menaggio on Lake Como. From Menaggio there are frequent ferries to Varenna on the other side of the lake. There's rail service from Varenna-Esino station to Tirano. The Varenna-Esino station is uphill from the boat dock, and I don't know about the availability of taxis; I only took that walk in the downhill direction, so I wasn't looking for a taxi. In mileage terms this is by far the shortest route to Tirano. How fast the trip is would depend on the schedules of the various transportation components.

A longer option would be to take a train from Lugano to Como, a bus to Bellagio and a ferry to Varenna. You'd then pick up the train to Tirano from the Varenna-Esino station as described above.

For fewer transfers you'd take a train from Lugano to Monza (just north of Milan) and switch to the Tirano train there.

At this time Google Maps is indicating the last part of the train trip to Tirano will be via a rail-replacement bus between Sondrio and Tirano. That would affect all the routes I've suggested. I don't know whether that situation will still prevail in September.

I think you can make one of those options work, if necessary. Worst case, you should be able to spend a good portion of the day in Lugano before heading off on one of the multi-transfer routes I've outlined above and spending the night before your Bernina Express trip in Tirano.

We are taking the Gotthard Express from Lucerne to Lugano on Sept 6th, spending the night, then are planning on the next morning to get to Tirano to board the Bernina Express which leaves at 13:17. We really do not have any wiggle room with our plans.

I did look into train schedules and I think it's possible to get there in time, but it will be an hour longer on the train vs the bus and probably not as scenic. Our Swiss Railway Pass will not apply to this ride.

I sent an email to the RHB but it has been 7 days with no reply, although they say it takes time to do so.

I did an ChatGBT and it suggested I go through some other websites to see if tickets are available, but so far it is too far out for it to show anything.

You've got time; I hope one of our more knowledgeable posters can come up with a good idea for you.

What time do you arrive in Lugano? Would you have time to move on from there to Como or Monza so you'd have less distance to cover the next day?

I can't comment on the comparative beauty of the bus route vs the train route to Tirano, but you will see lots of fabulous scenery between Tirano and St. Moritz.

We haven't booked the Gotthard yet, as it is too far out to do so, but was planning on getting in early evening to Lugano.
I saw where sometimes they open up another bus if it is a busy day. I sure hope so. I keep checking daily. Thank you for your suggestions!

This could be another case of tour operators, like Grand Swiss Train Tours, have sucked up the advance reservations. So maybe some will open up if they don't fully book by 30 days ahead.

The rail work around is not bad, with hourly departures with a train change in Monza, taking just under 4 hours. Could be equally scenic, as you will be traveling the length of Lake Como on the east shore, After Lake Como, you are traveling virtually the same route as the bus for the last hour to Tirano. Cost is only 15.50 EUR 2nd class, as you do get a small reduction with your STP covering you from Lugano to Chiasso.

Thank you, I feel better if I know there is a backup plan in case we can't snag bus tickets. The train ride will work if we come to that.