Best way to flush engine after rocker arm failure?

As to how to flush it, there's no way except to completely disassemble it, clean it like it just came from the machine shop (oil passages, etc.), and reassemble.
We lost a cam in our race car years ago and did this. It's a lot of work, but it beats always wondering if you got it all. A lot cheaper than building a new one.
Good luck with the problem, I'm no help there, but I agree with others, find out why they backed off.