My experience has been 100% were in stock.
I've placed about 10 orders at ToTW in the last 18 months or so, a total of perhaps 50 items, ranging from a Kentucky pistol kit to a bag of unplated screws. Everything I ordered was shown in stock, and I received my order complete within a few days.
For items not in stock, you can ask to be notified when the item becomes available.
When ordering on-line, you can see the complete order, which seems to me to be more convenient than reading off a list of stock numbers on the 'phone.