Soooo many machines! I've been collecting them for 5 years now, and I'm still missing some (BTW, the last time I bought a penny book there, they were closer to $10)
They had 4-6 machines in the area going from the parking garage to CityWalk (top of the escalators), some in all the big gift shops, and many out in the open. There's a Bubba Gump themed one just inside the Bubba Gump restaurant as well!
I use an empty M&M minis tube to hold change for pressing; a few of the big machines are sold as sets though, and will only take paper money as far as I recall. My youngest also got a pressed penny holder silicone bracelet in one of the shops.