Tahitian ukes are a pretty rare instrument so its hard to find places(outside the pacific) where you can buy or listen to them. Below are a few websites where you can purchase ukes and uke music online. You can pick up strings at your local fishing shop. Anything from 10kg-30kg guage line will do the damage. The best place to see live ukes in action are at traditional arts and culture festivals (see links). Local street markets around the pacific are also good places to find instruments and CDs for sale (along with plenty of cheap local food, clothes, arts and crafts and free entertainment). Heres just a few - Cook Islands: Punanga Nui markets in Avarua(Rarotonga). Aotearoa(NZ): Avondale, Otara, Mangere and Porirua markets. Tahiti: Papeete market.
(If you know of any other shops/markets/festivals please leave a message and I'll add it to the list).

CD's / MP3's