If you want to play a Gamecube game on the Wii, you need a Gamecube controller. Nintendo’s Classic Controller won’t do it. (Makes me wonder why they bothered releasing it, since you can use a Gamecube controller for Virtual Console classic games.)
Anyway, the youngest wanted one to play some Gamecube games, so we went hunting (in Melbourne). You can’t buy original Nintendo controllers retail now (might find them on ebay I suppose), but the (clone) options we found were:
Harvey Norman — corded, $30.
KMart — had nothing.
Dick Smith — cordless, $40.
EB Games — corded, $30 (not listed on their web site).
Game — corded, normally $24, on sale for $19.
JB Hifi — same as Dick Smith.
Big W — corded plus a Gamecube memory card (needed for Gamecube saves) $29.
As he wanted a memory card, and they appear to be pretty scarce, we ended up with the latter, which works well, though it would have been nice with a slightly longer cord.
It’s nice to know that (for the moment) you can still buy these things and play the old games. Viva la backwards compatibility.