In Australia, how can I get a Master Card/Visa Card which is loaded by US Dollars?

Hi guys, I am a student in Australia. I have some amount of US dollars and I want to use that for shopping from amazon and other US online stores. Is there any possibility that I deposit my US dollars in a bank in Australia and I get a Master Card/Visa Card by which I can spend my money without converting it to Australian dollar? I had a chat with an staff of CommonWealth Bank and he told me that they provide a service called “travel money card” by which one can spend other currencies including USD. However, in order to use that card, I should sell my USDs to CommonWealth Bank (at their buying rate) and then buy some USDs from them (at their selling rate) to load my travel card and because of their lower buying rate (comparing to their selling rate) I will lose some percentage of my money if I use their travel money card. I am wondering if any alternative service is provided by any Australian Bank (or US banks in Australia) which does not force me to convert my USDs to AUD. Any suggestion would be highly appreciated :-)