Every time a question on the "62" comes up the first thing we have to do is make sure what you are talking about. There is no such thing as a 62 Navy. There is a 61 round barrel Navy, but no 62 Navy. The 61 is built on the 51 Navy frame and has a six shot cylinder. The 62 Pocket Police is built on the 49 frame and has a five shot cylinder. What makes matters more confusing is that Pietta makes a "62" but it is actually a 61 full size revolver. Also, are you talking about a cap and ball revolver?
Bottom line bad news is there are no aftermarket lightened spring kits for the little Uberti 62s. Not really a problem because if you have the cap and ball revolver you really can't put a lighter spring in and get reliable ignition. (Believe me, I've tried.) If you are making it into a cartridge conversion, you can grind and polish your stock springs.