Welcome from Georgia, USA!
CZ 550's in .416 Rigby pop up from time to time on gunbroker.com.
I have one.
I love it!
My wife gave it to me 17 years ago as my 40th birthday present. I took a good buffalo and a baboon with it last August in Mozambique. (Both my PH and the assistant PH loved the CZ 550. My PH had one in 458 Lott. The PH in training was waiting on one in .375 H&H )
I was able to find good deals on ammo on gunbroker.
There seems to be a bunch of Hornady haters out there, but my PH told me that he had never seen bad performance on game with it, and it tends to be much cheaper than anything else you will find in the US.
My CZ shot solid and expanding Hornady loads, much more consistently (same point of impact) than any other brand of factory ammo that I experimented with.
My buffalo dropped within 20 yards, when I made an 80-yard heart shot through scattered brush with a DGX.
Feel free to PM me, if you have questions.