2S3 Akatsya. This unit's availability is set 2020, however it seems that they are no longer in Bulgarian service.
This site cites none in service,citing the Military Balance 2004-2005 by IISS.
http://www.csees.net/?page=country_s...try_id=3&sec=8
There's little in the way of sources that state exactly when the 2S3s were retired from service. The only sure thing is that they are retired.
I recommend setting the end date to 2004.
If anybody can provide a definitive sourced end date,they are welcome of course.