I'm pretty sure this is the only Bulgarian bill (or coin) I own. A quick check of Numista and the place where I store my bills reveals this is true. I got it around a year ago simply because it looked Soviet. When I got home I did a little research and found out it was Bulgarian, not Soviet. I was a little disappointed that it wasn't Russian, but it was still from a Soviet-era communist country so I wasn't entirely regretting this $0.25 purchace. It is worth about $0.50 which I was also a little disappointed about, but for $0.25 I got a good deal.
Here is an image of the watermarks used in this 1950's bill that weren't used in America until the 1990's.