Qantas does not sell passes. You can get them through various means such as reaching Silver FF membership, getting certain American Express/Qantas credit cards etc or flying the appropriate cabin on the day.

Be wary of passes bought on Ebay. Some are of questionable heritage and authenticity. Newer passes have conditions on them that prevent them being sold. Especially watch out for "Member's Guest" passes and similar. These are old cards which are most likely worthless now.

A friend can gift you an un-needed pass or two if required without any dramas. If you have any Qantas Platinum FF friends, they can get 2 guests into a domestic lounge (as well as themselves). For International lounges they can only bring in one guest.

If you go the Corp Membership route you should be ok. Phone up and sign up over the phone. You'll be given your FF number at that point.

(If visiting Qantas lounges) show them your number and they can look it up on the computer. Identification might be required. It should also print out on your boarding pass that you're a Qantas Club member.

(If visiting BA/AA lounges) then request Qantas issues you a temporary card or some other proof of membership. I'm not sure what they can do in this area.

I believe Qantas are fairly quick at sending out new membership packs to Australian members. I also belive you can get them to express deliver the pack for an additional fee.