We buy our durian from Asian Grocery Store in Sunnybank... we're in Canada right now on holiday, so I don't have the exact name. It's on Main Street, in the opposite corner to the big mall (the first one you pass after coming down from Kessels Road - it's called Kessels when I get on it in Mount Gravatt and the name changes often). The Asian grocery store in the mall there also often stocks durian. Expect to pay $2.99 per kilo for frozen durian.
I think that Chinatown in Brisbane would be worth checking out too. We'll be doing that early October when we get back. I never thought to before, but Chinatown in Toronto Canada is packed with interesting tropical fruit (tamarind, mangosteen, young coconuts, 5 types of mango, sweet sop, and funky types of fruit I've never before seen).
Tropical Fruit World (Gold Coast)
http://www.tropicalfruitworld.com.au/http://www.tropicalfruitworld.com.au/learning/ftd_all.asp (tropical fruit directory)
I can’t find the website for the tropical fruit tasting place in the Daintree right now, but if you go visit there add is everywhere. There's also a tropical fruit icecream place - we passed on the ice cream and convinced them to sell us fruit instead!
Cheers, Sheryl