FAR-23 commuter aircraft aren't required to publish Vmcg as long as a Vmc is published. If so, V1 and Vr must be higher than Vmc...no reduced V1 possible. The designer may decides to certify the aircraft with a Vmcg (to reduce runway requirements on wet / contaminated runways), but obviously has not for the B1900.
All FAR-25 aircraft must publish Vmcg / Vmca.