I also went to this Rtm &amp; Beer festival on Saturday. I tried 3 different kinds of beer and I also liked the music, too bad it was raining almost all the time.
As to Harmonica boza you can find it in Piccadilly markets as well.
And last but not least - you are slowly turning into a proper Bulgarian Kiki - you're one step closer to eating breakfast which includes banitsa and boza. You shuold try this classic combination ;)