Very few on the scene in ADL - I've been looking for ages also. And unlike our US counterparts, the $10 enlargers are like pigs flying; if you are lucky enough to find one for that price, you definitely deserve a medal!
Total Photographics are the guys I'd suggest as well, although they have had nothing in the way of 5x4s for quite some time. They do have the final edition of the Photographic Trader (RIP), which often had 5x4 enlargers listed. Pretty sure it had some listed, but can't remember prices off the top of my head.
The Melbourne option is a good one, a day trip could land you a nice souvenir. . . . . .