I think they were both found but I could be wrong. If I did purchase one, it would have been from Crock or Sadok because I know I had it long before I met Bela or Ferro and I can't think of anyone else who would have carried such an item. As for where I might have found them...I am pretty sure they were monster drops.
I just looked at the itemtable list that Obverse Reaction hosts at
http://www.accessv.com/~cpommer/itemtable.txt and found the Filcher's Band listed as possible treasure in the Monastery Wheel Room chest, Nessie's chest (Davy Jones' Locker), and in the "Sea Caves Good" which I suppose means you might be lucky enough to find it in one of the chests there. I didn't see it listed on any particular monster drop but that doesn't mean that's not how I got them.
