The Groumall class of military freighter was commissioned by the Cardassian military logistics division to provide logistical support to military outposts and bases across the Cardassian Union. Designed and initially manufactured by a private consortium, the Groumall class was sold to a number of empires including the Klingon's.
Released in to service by the 2370's, the private consortium that designed the Groumall made it modular enough to fulfill a number of different operational needs by making the ship modular. As such, Groumall vessels could undertake roles such as cargo transport, scientific exploration, troop transport and even undertake limited patrol activities when fitted with a weapons module.
These are from Shapeways and have been painted up to serve the Klingon Empire. You can find them here (and are called Kromag on Shapeways). I had them printed in Frosted Ultra Detail.