Typically the 6 main kaon decay modes, beam pions, beam protons and K+→ π+ ν ν are available in two variants: standard decay region (102-180m) and extended decay region (102-265m), for trigger studies. Other samples are available on request.
The MC files are easily accessible at CERN (twiki).
Test productions at CERN
The MC files are placed on CASTOR /castor/cern.ch/na62/offline/mc/prod; a replica of the most recent ones can be found on EOS /eos/na62/data/offline/mc/prod
It usually consists of 1M events for each of the 6 main decay modes and the signal, with the addition of halo muons, 100M beam pions and 100M beam protons.