Obscure ingredients are, understandably, hard to find. Grocery stores don't typically have buckets of glucose or packages of crunchy feuilletine on their shelves. You could spend all day running around town looking for these things.
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