Making your own islands is seriously very easy.
Go buy some styrofoam insulation in about the thickness of the islands you want and some white glue from a hardware store. Also pop into a hobby store and pick up some green flocking and foliage (moss).
Using a sharp knife cut and shape the styrofoam into the desired shape. You can use the white glue to stack some pieces for higher islands if you want, but it really is'nt nessary. Time: Depends on the islands, but about an hour.
Thin the white glue down about 3/4 water and 1/4 glue. Use an old paitbrush or rag to cover the entire top of the island. Set the island in a box and dump green flocking in to cover the island. Let sit about 15 mins and take the island out. Reapply the glue mixture to some of the thin spots and reapply the green flocking. Then with 100% white glue, attach some of the moss in corners, or in a patchy cover pattern for a forest look. Time: About an hour.
Let them sit overnight to dry completely. They will last years if stored properly and not abused.
There are a ton of websites that have photographs and even more detailed instructions. Give it a go, its seriously very easy.
Peace