That's why Christina Tosi says to skip the fuss and head straight to the internet. Amazon is a one-stop-shop for all these ingredients.
The only downside is the shipping cost. Many of these items are sold through Amazon but shipped by a third-party, which means paying for shipping on each individual item. My recommendation is to gather a few friends, make a big order, and split the cost.
Here are just a few of the ingredients I've found through Amazon:
• Cacao Barry Pailletes Feuilletine, $54 for a 5.5 lb bag
• Caullet Glucose Syrup, $11 for a 2.2 lb bucket
• Valrhona Cocoa Powder, $13 for 1 lb
• Just Tomato's Just Corn (Freeze-Dried Corn), $24 for three 8-ounce packages
• Get the Book! Momofuku Milk Bar by Christina Tosi, $18 on Amazon