The first stamp pictured was part of a controversial set released in 1921.  They were actually ordered and printed in 1917, and contained scenes from the Bulgarian countryside.  They went undelivered to to the war in Europe at the time -- and by the time Bulgaria released them, some of the territories pictured had been lost to Romania, Greece and Yugoslavia.  Finally issuing these stamps in 1921 might have made financial sense -- but prompted a harsh political reaction from it's neighbors who saw them as incendiary propaganda,  They were withdrawn fairly quickly.  Interesting article here: https://www.linns.com/news/world-stamps-postal-history/bulgaria-1921-world-war-one-set-ferdinand-czar-allied-powers.html

The example I have posted may be unused (MH) -- I don't see any traces of a postmark, and the back appears to have some gum, but I am not entirely certain; check the photos carefully before you bid. 

The second stamp pictured is one of a nine stamp set issued to honour a British journalist, James David Bourchier (1850-1920).  Interesting article here: https://www.linns.com/news/us-stamps-postal-history/2014/october/curious-1921-bulgarian-stamp-set-worth-acquiring-f.html

The third stamp -- is nothing so special.  issued in 1960