I have used a soft case once, but have mostly used cardboard boxes. I never had trouble finding one, but most often I just leave my bike with a bike shop and pay them to pack and ship it home at the end of the trip. They typically have charged me $40-60 and the shipping home was another $40-60. I found the ~$100 to be worth it to me to not have to deal with packing and lugging the bike to the airport.

BTW, I thought that a lot of european airlines allowed you to just wrap it in shrink wrap. I know I have seen quite a few pictures of bike tourist checking their bikes as baggage that way.