G'day mrmouks,
The permit simply allows you to keeper specified native reptiles. It doesn't give you blanket approval to keep whatever comes your way - you need to keep fairly detailed records of what species it is, who you purchased it from, and complete a Movement Advice the details both your particulars, and the person you are buying from/selling to.
It sounds like the snake isn't covered by any paperwork at the moment, so your best option is to contact the EPA and let them know what the situtation is. They are very open to this sort of thing - if you co-operate with them, they will return the favour and sort it out.
Cheers