Geek Exchange has lovingly complied a list
of many of LucasArts' best loved older games and linked to the best places to purchase them. Some of the games are probably easier to find in the UK, Australia and New Zealand due to the relatively recent Activision re-releases
under the LucasArts Classics banner.
It's the sort of thing we should probably do here at Mojo someday. Until that day though, enjoy Geek Exchange's hard work
Feel free to add to the list in the Comments section if you know of more places to legally obtain these, and any other classic LucasArts games.
Source: Geek Exchange