Never had them, and never will, considering how they're collected. Apporximately 95% of the world demand for frog legs is from wild stock. Worldwide, from 1987 to 1997, an average of 4716 metric tons of frogs were collected annually (but neither China or Vietnam are included, two big frog (leg) export countries). Between 1998 and 2002, 5.2 million kg and almost 15 million individuals were collected imported to the US, where everything was declared as wild caught (and used for frog legs).
Just something to consider...

Information taken from Extinction in Our Times: Global Amphibian Decline