We'll be going for the first time in a couple of weeks, so I researched this, as well. My son loved doing them at Disney.
There are penny press machines at both Universal Studios and Islands of Adventure, as well as in the parking structures that connects to the parks, and in CityWalk.
Unlike Disney World, Universals on-site hotel resorts do not have penny press machines.
Here's a list I gathered (it's long!)-
In Islands of Adventure:
Located inside the queue line for the Hulk coaster.
There is a new machine in the Lost Continent located across from the Magic Show/Shop. The machine is across the midway and not facing the midway directly.
2 machines in the Spiderman Gift Shop
Machine in Spiderman Ride line
Hulkcoaster exit line
Kingpin Arcade
Adventure Comics
X-Men shop
Near the Times board, across from Confisco Grill
Treasures of Poseidon
Jurassic Outfitters had 3 machines
Dino Store
DeFotos Expedition
Toon Extra
Betty Boop Shop
Gasoline Alley- near restrooms
Trading Company has 2 machines
Port of Entry 1- Popeye
Port Entry 2
Snookers and Snookers Sweet Candy Cookers
Circus McGurkus
Cat in the Hat Ride
Cats Hats and Things
Mulberry Street
Dr Seuss Machine
Fantastic Four Machine
Bubba Gump Shrimp Co- CityWalk
Nascar Sports Grille- CityWalk
NBA City- CityWalk
Universal Studios:
On Location Store (outside by picture pickup area)
Universal Studios Store- 3 machines
Simpsons Ride- outside Kwik-E-Mart
Horror Makeup Show
Shreks Ye Olde Souvenir Shop
Shrek Photo Pick up/donkey photos
Revenge of the Mummy
Aftermath- Twister Gift Shop
Restrooms by Richters Burgers
Jaws- Midway near Disasters ride (may be gone now)
Broadside Midway games near Wave Roll
MIB Gear Shop
Barney Store
Cartoon Store (may be 4 machines)
Lucy Tribute
Terminator Cyber Image Gifts
Its a Wrap Store
Rip Ride Rocket
ET Gifts
Hope this helps!