I'd try to flesh this out a little more. Most don't consider Australia an island any more, though I see in this case you are including a number of Australian animals. There are, however, a lot more areas you could look to find some great options for island species. Assuming this is a US zoo, some ideas to consider are:
- Japanese macaques
- Galapagos giant tortoises
- Northern Sulawesi babirusa (Sulawesi)
- Visayan warty pigs (Philippines)
- Binturong (Indonesia and the Philippines)
- Matschie's tree kangaroo (New Guinea)
- multiple options for iguana species (Caribbean)
There are also A LOT of options for birds that can be included, so I'd definitely look into adding a walk-through aviary or something of the like. There are a lot of Asian columbiform species that'd be great choices for this, and also a number of waterfowl (e.g., Madagascar teal, nene, Philippine duck), amongst other species. Herps is another area you can get a lot of island endemic species, particularly smaller ones.
I'm assuming you are using Humboldt penguins and California sea lions as stand-ins for other species? Neither are commonly associated with islands.