You could try Ebay for the moulds.
Then any Art shop has light plaster of paris which you can use to make the casts. It's very simple and you get a good result if you have the right sort of moulds.
there was a programme on RTE1 last night about a woman in kerry launching a new business. She makes personalised minature people for wedding cakes, but I suppose they aren't really limited to just cakes!