There is a lot of communist kitsch in Sofia. Up by the Nevski Church there are tons of communist relics of Stalin, Lenin, hammer and sickles, and red and gold junk. In Koprivshtitsa there are antique dealers who sell lots of old Bulgarian Communist Party paraphernalia and army medals and coins with Georgi Dimitrov or Blagoev, the father of communism in Bulgaria, on them. A few years ago many T-shirt shops in places like Plovdiv, Varna, or Sunny Beach sold Soviet Union T-shirts. The younger generation in Bulgaria does poke fun at the communist past. The rap group Upsurt featured Todor Zhivkov's picture and an clip from one of his speeches in the music video "3v1".
I agree with you that Bulgarians haven't really done a lot to publicly condemn or remember  communism like the Czech Republic or Hungary or Poland. But there wasn't a huge underground resistance movement in Bulgaria either. Bulgaria changed by default, not from public pressure. I remember a historian writing something like, "Nowhere in Eastern Europe did democracy come faster, but less sincere, than in Bulgaria." The power structure in Bulgaria remained the same after communism. The Bulgarian Communist Party and the Bulgarian Secret Service were two of the most tightly-organized groups in Eastern Europe. It's no accident that the huge statue of the Soviet Army still stands in Borisova Gradina. The Bulgarians who benefited from the communist regime are still in power today and there's no way they are going to attack the system that supported them. Also, the average Bulgarian probably didn't like the communist regime, but at least he or she lived better. Bulgarians received rights and freedoms, but saw their economic freedom disappear overnight.  I think if you look harder you will see the younger generation poking fun at the past, but not with the same vigor or passion as those in Central Europe.