Doing pull-ups by holding on to a gi will get your grip nice and strong.
Tie a belt around a tree or pillar and train some throws.
If you can afford it, invest in a throwing dummy, but they are mucho $$$
If you wanna train breakfalls, outside is the best way- grass and in this case, snow.
The thing is, while you can develop some of the atributes needs from judo alone, you won't develop any of the skills.