Yeah, I'm pretty sure that particular area has an infinite supply of them. I don't know if this was intentional or not. They literally respawn within seconds.
It's good stuff too. Wyvern leather has similar properties to dragon leather, except it's blue instead of white. And we have an infinite supply. Unless you use the dupe glitch, dragon stuff is very limited. Good thing silverite and great bear leather are easy to find. (no, I'm never going to tire of that stuff!) Leliana's gather leather mission gives a steady supply and Emprise du Lion has lots of silverite. (Highgrove camp leads to Alphonse's passage, where lots of dawnstone and silverite can be found. Bloodstone too, but it's tier 2. Dawnstone and silverite are tier 3. Aww, yiss!)