How do you know if that's all you need? And where do you get one?
CHRA is everything BUT compressor cover, exhaust housing, wastegate. If the wastegate still works (likely) and the compressor cover and exhaust housing are still in good shape (turbo didn't get loose enough to where wheels hit) then you should be good to go. From what I see of yours it still looks OK but taking the covers off before buying anything would be the smart choice.
Something like this. You might be able to change it without even removing the exhaust. I know I could do it on my high mount 200TDI.
This is a CHRA
Where to buy?
LRD for new turbo
There is Turbo Rebuild UK or Melett that offer CHRA's. I imagine other vendors can get you something too.
When mine goes I have been weighing springing the money for the Allisport ($1200?), the upgraded billet wheel Turbo Rebuild UK ($400), or just a new Garrett ($500). I have my truck running so damn good now I almost don't want to mess with anything. It starts right, no smoke, enough power to pull to 85mph or "comfortably" cruise at 70.