Who stocks the stuff?
Short answer…
Nobody, not even JnJ. Longer answer, Walthers has a reasonable selection. JnJ himself has a good selection. He does thing in batches and Walthers buys in batches, but the creating and purchasing may not be in sync. Which means it can end up that Walthers has things JnJ doesn't have anymore and JnJ has things Walthers didn't choose to purchase and couldn't purchase when it was time for them to make a JnJ purchase.
(Since Walthers only buys from their distributors on a schedule that only makes sense to Walthers, how else can they put things on sale for 2 months but never actually have any in stock the entire time?).
To find out what Walthers has in stock do a advanced search and use manufacturer 344, pick the in stock checkbox (or you'll find yourself wanting things that aren't in stock) and 300 as the count and you should get 70ish items.
You can also email JnJ and ask for specific items, he take a bit to answer but does seem to be good at answering anytime I sent an email.