Microsoft has not announced the Surface Mini officially. But it seems one accessory maker already has a case and keyboard for the device. Microsoft does have an event scheduled for May 20, so we should hear more about the Surface Mini then. Nevertheless, you can order these Microsoft Surface Mini accessories today and get them on May 28:
VSTN Bluetooth Keyboard Portfolio Case: a protective case plus a detachable keyboard for the Surface Mini. It gives you access to all the ports and controls.
Surface Mini Smart Cover Case: fits the Surface mini but has cut outs for all the ports and controls. The front flip is foldable and holds your tablet at the right angle.
It does seem that Surface Mini will ship by May 28, at least that would be my guess. Whether it is worth picking up is a whole other story.