If it is a literal newt's eye, even Flesh to Stone doesn't fully solve the logistics problem- you're still going to need a reasonably skilled stonecarver to extract the eyes from your petrified newt. You could try removing the eyes first, I suppose, but at that point the eyes would be objects rather than creatures, so they wouldn't be valid targets for Flesh to Stone or most creature-specific petrification abilities.
Finding one naturally would essentially require some novel arcane/natural history explanation, given the rarity of fossilized soft tissues, and even if such a high quality newt fossil were found somehow, it would a.) present the same issue as Flesh to Stone and b.) be much too rare and valuable to dismantle for low level spell components. Maybe there's some way to artificially replicate the process under highly controlled conditions, but I imagine the time required would be prohibitive.
Probably the best solution would be some sort of homebrew spell. Transmuting a few grams of nonliving flesh seems like it should be possible at a lower level than 6th, even if there's not a published spell designed for that purpose.
Of course, any of these methods would be an absurd amount of effort if you didn't already have some very specific reason to want a petrified newt's eye. Which leaves the question: How in the world did anyone figure out that it worked as a material component?
