You can do it this way.
Find all Czech people who have hidden virtuals and how many in Czech Republic:
Select Top Hidden, Cache location Czech Republic, only people from Czech Republic, add filter Cache Type Size and select virtuals:
= 32 cache owners, one virtual each, hidden in Czech Republic.
Compare this to the same query with Cache location set to blank (anywhere in the world)
=33 cache owners, one virtual each, hidden somewhere in the world.
Comparing the lists I see that only ufemezumik has placed a virtual outside of Czech Republic. You can identify the cache itself by looking up his Geocaching profile (it is GC7B6YN in Iceland). (but then, it is your cache!)