Vindictus Wiki is what i use to see where things drop, some use Vindictus DB - Home but i dont like them because you have to scroll to see if people confirmed this and that, bleh.
took a look for myself, and the sewers seems to be the only play they drop, that sux.
quoted from https://www.vindictusdb.com/]Vindictus DB - The best place to farm Digger Spines is Wet, Dark and Mossy. There is a bonus mission in Where the Road Leads for Bloody Thorn, but there are only 9 Digger Spines in the map, and there's only a 50% chance that you will get the map that has Digger Spines on it. That makes it very unlikely that you will be able to complete the bonus mission, as Bloody Thorn is the rarest item Digger Spines drop.