The VZ-52 was made from 1952 to 1956 in 7.62x45,a caliber unique to the Czechs.In 1957,and at Soviet insistence,it was converted to 7.62x39 to conform to the Communists wish to standardize calibers in Eastern Bloc nations to the ammunition used in Russian weaponry(SKS's and AK-47's).
It thus became the VZ-52/57,a much more rare and valuable rifle.
52/57's in Very-Good condition sell in the $500-$600 range (October 1998) compared to the much more common VZ-52's in the $100 range.
I believe the 52/57 was only made until 1958,when the Czech's then came out with their own version of the AK-47 known as the VZ-58 (shown below)which used the 7.62x39 round.
Many VZ-52's were stored away by the Czechs and then given out to various emerging third world nations friendly to the communists(Cuba,Grenada,Palestine,Egypt and many others).
I think the reason there is so much surplus ammo for them is that the Czechs never used them in war.It was one of those situations like the Bulgarian 91/59's,"They were made,then stored away for the invasion-That Never Came!"
Only later did they see combat elswhere-- like in the hands of Castro's guerrillas.In fact,I remember seeing a show on the History channel with a shot of Castro,relaxing,holding a Vz-52 in his arms!
If you have a Vz-52 now,enjoy shooting it,but stock up on ammo.Last time I checked Century had it on sale cheap.They have something like 90,000 rounds of it.But no one makes reloadable brass for it yet,so when it's gone....it's gone!