garmin gps help needed

Hello bushwalkers. We came to Australia to do some walks. We have Oz Topo maps for our garmin gps on a micro sd chip but we forgot the chip at home. Our bad! We'd like to download the Shonky maps to use on our gps but we don't have the necessary s/w or Windows programs. Any suggestions? Right now we're in Bathurst and heading northish. We are willing to buy garmin oz topo 3 maps but do not know where to by them on short notice. Any suggestions? Thanks, Liz