Actually this was one of the mechanisms I used to employ for 'side quest' generation when I played. All low level material components were readily available in Marketplaces etc, but the more esoteric stuff was something the guys n gals had to go look for....
This prompted some great ad libbing (and frantic prep from me) but really livened up the whole experience.... until some clever so & so decided that surely other spell casters had these ingredients........ and then proceeded to form an 'arrangement' with the local thieves guild..........
Players... cant live with 'em... so throw in a Hive Mother Beholder !
