A silly question, but: where am I most likely to find them? On 3rd floor and got a great recipe using them. I sold my last ones long ago. Now I'm trying to go through Level 1 wizardlands and transform every being there.
Why I hoard at least one example of every basic item I've found - what are you trying to make, Rubber Pants? You could potentially find those later on, for sale or as a drop. Otherwise, it's up to the RNG god. As far as I know, they'll never appear in a vendor machine - it's either Brax, or luck.
Bangomkiigorlech is DL1 and has adventuring pants. Lately, I have been putting everything I find in the google spreadsheet here: https://docs.google.com/spreadsheet/ccc?key=0Alj_-ATA7GiYdGdDempHZEV5eUN0Y2VKRG1sazk5Nnc#gid=2 I was playing Easy mode without permadeath on Windows XP with the Steam version of the game and I hadn't been to DL2 yet. Most likely, you will find the adventuring pants unless you wait for the new patch to come out. I hear some things will change with the new patch so you might want to grab them while you can.
