A single core set includes all 6 obstacles (1 space station, 2 debris fields, 3 asteroid fields). You can get acrylic versions from third party companies like Litko. There have also been some really cool 3D versions created by individuals using real rocks and other bits of plastic ships. I'm no where near that creative. And, those are hard to navigate around in an actual game. You can't really set your ship down on a giant plastic asteroid.
I occasionally use my Space Rocks set of 3D terrain (impossible to find anymore as they were rightfully sued into oblivion by FFG) and it works just fine. You use a clear acrylic overlay that goes over the flat cardboard obstacle. If a ship or squadron would need to use that space, you simply remove the overlay until it's clear again and then replace the overlay with the 3D elements. Easy peasy.