A couple of possible suggestions as these grenades seem very hard to get at in the UD if you're not a rogue, and especially if you don't sail.
A special rogue merchant that sells them, maybe somewhere like the thieves den in the shadow plane, or just various merchants in rogue-ish places.
More mobs in the UD that drop them. I haven't found them off any mobs in the UD. They only show up in chests (disjunction shards usually and very rarely), or on pirates when out at sea.
Give Vigilante access to the -rogue command with Complex Experimental Device Method.
