Hi,

Your commercial license may help but is not sufficient to fly solo. More important to bring your log book. To fly here requires you to be a member of the GFA (Gliding Federation of Australia)and a club. To fly solo will require most likely a number of check flights, number depending on your proficiency.
Lake Keepit is certainly an excellent recommendation. Cross country soaring is possible all year around and March is only late summer there and flights to 500 km in a moderate performance glider possible. Good accommodation available on site.
If you come to Melbourne there is still some good soaring to be had in March. Benalla, 250 km north of Melbourne, operates 7 days a week in summer. If you are restricted to weekends, come out to Bacchus Marsh, 60 km west of Melbourne. 3 clubs operate there on weekends and public holidays. Bacchus is not the best cross country site in Australia but I did a few flights from 100 to 400 km out of here last March.
Where ever you decide to go, I'm sure you will made to feel welcome.
Rolf