Any tips to getting that Shiny Karp?

It's just random. I got my first one after the event, it was the 450th or so since they came into existence

Best advice I can give you is click every karp you see!

In my area, there is a canal where Magikarps spawn like Pidgeys. Find something similar in your area?

just gotta grind.

All you can do it sacrifice many Karps to RNGesus.

Good luck.