It's the wrong time of year now, but ideally you need to either collect some eggs after getting permission from the land owner, or find someone who would post you some eggs from an existing garden population. If I were you I'd place a wanted add on here and anywhere else you think pond owners would see, that's how I got my Smooth newt colony started. I have even seen adds in the back of gardening mags in the past for native amphibian eggs.
To be clear though, this advice only applies to Smooth and Palmate newts. If you suspect there might also be Crested newts in the pond give it a wide berth, disturbing them in any way is against the law.