kathyNJ, I've come across some moneygami kits with special practice bills, but I think any paper will do as long as it is not a square sheet. You can start practicing with a sheet larger than a real bill if you're a beginner and then proceed to folding real-size ones.

Sleepy13, Here's a Lily tutorial https://www.youtube.com/watch?v=UnIYqlcWuDs. Hope you'll like it. I made it last year for my brother's bday.