A 13.8V power supply will probably work. Even though the current is rated at 800ma, I'd go for something higher 1A or even 2A ....... your (whatever it is, I have nfi

) will only draw the current that it needs. A higher current rated power supply will run cooler than one rated at exactly what you need.
The voltage is more critical, but high quality gizmos will have a degree of latitude, and have internal circuitry to convert whatever is going in, to whatever it needs. Just make sure that the polarity of your plug is correct otherwise you can completely roger the circuitry. Having said that, most quality equipment will have protection circuitry or fuses anyway.
I use GME 13.8V power supplies for my radios and have been very happy with them. If you look on EBay for power supplies -> radio equipment you should be able to pick up a 2A job at a reasonable price.
Otherwise, as previously suggested, Jaycar is a good source... Also try Altronics
http://www.altronics.com.au/
Oatley electronics may have some
http://secure.oatleyelectronics.com//index.php
as may Wiltronics
http://www.wiltronics.com.au/catalogue/
Cheers
Tim R
Oh, by the way, if you still have the old one I may be able to help you get the old plug connected properly onto a new power supply ...... pm me if you get into trouble