1,000 unikarps I believe is the published figure.
As for whether this is the second rarest Magikarp, I’m not sure. If it’s true that the Lucky Award 2002 colouring contest awarded 50 unlimited boxes of the Pokémon-e Starter Deck in Japan (see this post), an unlimited e1 Magikarp could even be rarer than the Snap contest card: Each Pokémon-e Starter Deck came with 8 random cards out of the first 32 cards from Japan’s Expedition Base Set. One of those cards is Magikarp, 012/128. That means there’s was 25% chance of an unlimited Magikarp being pulled from each of those 50 unlimited boxes, meaning statistically only 12 or 13 of those exist.