The link works for me. It’s a pretty short JSON so I posted it below:
{
"tilejson": "2.1.0",
"format": "heightmap-1.0",
"version": "1.1.0",
"scheme": "tms",
"tiles": ["{z}/{x}/{y}.terrain?v={version}"],
"attribution": "© Commonwealth of Australia (Geoscience Australia) 2014, Data: SIO, NOAA, U.S. Navy, NGA, GEBCO, Geoscience Australia",
"projection": "EPSG:4326",
"bounds": [-180.0,-90.0,180.0,90.0],
"available": [[{"startX":0,"startY":0,"endX":1,"endY":0}],[{"startX":0,"startY":0,"endX":3,"endY":1}],[{"startX":0,"startY":0,"endX":7,"endY":3}],[{"startX":0,"startY":0,"endX":15,"endY":7}],[{"startX":0,"startY":0,"endX":31,"endY":15}],[{"startX":0,"startY":0,"endX":63,"endY":31}],[{"startX":0,"startY":0,"endX":127,"endY":63}],[{"startX":0,"startY":0,"endX":255,"endY":127}],[{"startX":0,"startY":0,"endX":511,"endY":255}],[{"startX":0,"startY":0,"endX":1023,"endY":511}],[{"startX":1666,"startY":261,"endX":1900,"endY":455}],[{"startX":3333,"startY":523,"endX":3800,"endY":910}],[{"startX":6667,"startY":1046,"endX":7600,"endY":1820}],[{"startX":13334,"startY":2093,"endX":15200,"endY":3640}]]
}
``
You can also look at the CesiumTerrainProvider source to see what it’s doing with the availability and all that: