I don't think your Gemeinde will do that. You need a notary (look up "notariat" for your local one). Having said that, they aren't normally open for business at the weekend.
Depending on what the Australian authorities will accept, maybe you could call them and ask if you could just get a lawyer, doctor or judge to sign off for you today (if you can find one).
Actually my "Gemeinde" in Germany did that for me. I asked my husband and he said that the Gemeinde here would do it, no problem. He also said the police would also do it. But he suggested your best bet would probably be to get the Gemeinde to fax it directly to the destination or even the post office should be able to stamp it as a certified copy and fax it for you. Good luck and have a nice weekend
This user would like to thank Puhutes for this useful post:
The question is who can certify the doc and put the notary's stamp on rainy morning of Sat. Would check yellow pages and call private attorneys. Make sure you pay visit before 18h00 though otherwise it might get ugly