Again, second time answering this in a few days, it's long since been established that 450 recipes are random product drops on merchant and break up gangs. It's been well over a year since that's been known and at least that long since I first found two recipes on break up gangs on w4.
Edit:
This is where I first suggested recipes as a separate category in May 2011, and it wasn't long after that it was decided they were random products. My trader has 48 450 recipes, only one of which is the saddler 450, so that might explain why I had so much trouble finding it on w16, it's apparently not a random product like the others. Many of those were found with regular items and I've never seen one drop with a regular item on any other job but those two, except for possible white water, but I can't remember for sure on that one.