It appears you can only buy these tickets two month in advance , correct?
I am looking for June but it only gives me April and May. Just confirming. Thanks
Yes. Try again tomorrow (April 1). I purchased mine at the beginning of the month.
I just walked up and got mine without any lineup at all. Go first thing in the morning.
If you want to be sure of the first time-slot or not needing to wait around at other times of the day, I would not count on just walking up. In August 2016 the tourist office recommended that first-entry-time tickets be bought 48 hours ahead of time; I only needed one ticket and didn't want to ascend a tower. I understood the staffperson to say that 24 hours ahead should be sufficient if I was not picky about the time. I wouldn't count on Barcelona being less busy in June 2018 than it was in August 2016, and I have no idea how desire to do one of the towers would alter that advice about timing.
June is high tourist season in Barcelona. We went in March and had reserved tickets for when the church opened. As we were touring the church about an hour later I looked down on the walk-up ticket window and the line was long! Best just to reserve your tickets now. Very easy and convenient. I just downloaded tickets to my phone and the employees scanned them before entering.