Looking around, I've personally been rather impressed by the performance of the Romulan Vendor Only supplied Plasma Repeater Pistol and the corresponding Plasma Piercing Beam Rifle which for some reason can only be obtained from a single NPC Vendor in the Romulan Command Center on New Romulus. To add insult to injury, these Common Only weapons only extend their Mk # up through IX. There are no Mk X, XI or Mk XII versions of these uniquely ROMULAN weapons (or if there are, I haven't found them yet).
Check the C-Store.
Edit: My mistake. Dilithium Store.
Last edited by questerius; 10-19-2013 at 08:26 AM.