mcgyr is right, your location is a big consideration for this one, especially if you're looking for ones locally. Nevertheless, you could always rely on online sources such as eBay, amazon, and the like. Anyway, below is a site with reviews that appeared when I searched Limewood Airstone Supplier, check this one out yourself:
https://www.marinedepot.com/Oceanic_...AQRPOT-vi.html
Hope this helps!