You don't need hills for hill training, anywhere where you can pedal between 4-5w/kg for 20 mins would be the same as pedalling up a hill.
Being fast in hill country isn't just about going up hill also you have to descend well. I have cycled with people who trained on turbos and stuff like that and they could climb very well but I soon discovered that after they had left me behind on the up (I was heavier than them by at least 10kg) I could catch them going down very easily because they were burning their brakes all the way down. These were Pyrenean hills, the longest was 32km.
And mental strength is important. I cycle in the Limousin and it's all hills and I get to the point where I can't even remember cycling up them, I just do it. It's only when I am tired that the prospect is alarming.
You can only train for hills by cycling up and down them and even then, all hills are a bit different. Some hills you have the sun on your back, no breeze, no shade, others you find a snow storm at the top and have to descend whilst wet and freezing and still have to be able to brake for hairpins.