what can I use instead of egg and milk to make pancakes with buckwheat flour?

Ground flax is often used as an egg substitute in pancakes. I don't know the ratio off hand, but any really good vegan cook book will have it. Vegan a go go by Sarah Kramer has the best list of egg substitutes I've seen.

As for milk, I would go for almond as it's most traditional and easiest to make at home if you have raw almonds. However, just about any milk substitute will do.

Are you looking for a vegan pancake recipe? There are lots on the web. Many use soy milk but you could probably substitute almond milk.