Yes, that should have been Bonev. His death is described in Stoyanov's book "We defended you, Sofia". As far as I know it is undergoing preparation for a fourth publishing (this time not censored as was before) and I'll try to get a copy.
There are two other book with memoirs of Bulgarian fighter pilots which could provide info, Todor Rozev's "Memories of a pilot" and Mihail Grigorov's "Eagles of Bulgaria". Sadly, both are very old, censored and hard to find (they haven't been published since the 1960s).
Here's a few links with the victories of Bulgarian pilots, including Bonev.
http://hometown.aol.com/bogdanovasla...bats_1944.html (note: includes only those up to 11th June)
http://hometown.aol.com/bogdanovasla...ianPlanes.html
http://forum.12oclockhigh.net/showthread.php?t=14516