I don't know puppet so I don't know it's input requirements, but I'm not seeing the issue. iptables (on Linux) accepts CIDR blocks as arguments to --source and your input is CIDR blocks, how about print or say?
As for the other, less obvious "question" (Given a CIDR block, how do I see who owns it?), all that comes to mind is brute force: look up each and every IP address in each of every CIDR block. The reason you need to do ALL of them is because people who sell hosting resell individual IPs from from CIDR blocks. On the other hand, you might find some of ARIN's web tools of use, if you're not worried about being wrong sometimes (e.g. resold IPs).
Even if he is getting a bit snarky, I agree with boftx that "you're a saint, you shouldn't have to be reminded to give examples of input and output."
