These are fairly common in Grauberg (S) in the southern regions. Be careful when coming up on a harvesting point, however. Chigoes can often be found near many of these points.
They were NPCing for around 750 gil. Your best bet is to keep them in your mog house until you have a stack and sell the lot. If you sell individually, you can expect to see one or two sell per day on average.
