The only problem with chancing upon genetic anomaly like that is that it's like trying to find a off color needle in a pile of thousands of needles. The odds of finding the one you need would be astronamicly low, not to say it can't be done but you'd probably have a higher chance at finding a pearl in your seafood or finding a $100 bill out on a walk. Genetic engineering would be the easiest/sure fire way to accomplish this.