I'm not sure how strict Melbourne and Monash both are, but given that you got over the required ENTER (well over in Monash's case), your methods score was only one point out, you did respectably in further maths this year, and you've demonstrated your aptitude at commerce with your PWC award, you might be able to plead your way in.
Bridging courses may also be a good idea. Given that you have an okay maths knowledge already, you may be able to finish one over the summer. If you decide to enroll in one, inform them. Open Universities offers some that you can do at home and I'm pretty sure you can pay off the course fees (which aren't very high in the first place) through FEE Help, here's a link:
https://www.open.edu.au/wps/portal/cxml/04_Sj9SPykssy0xPLMnMz0vM0Y_QjzKLN4h3NQTKRJoDWUG--iH6UfpR-aWJoXmZJc75Kan6kaF-PsZG-gXZiZEAGWh0BQ!!
You can start these unilearn bridging units any time and choose to do an optional exam, or not. You have up to 12 months (from the date you enrol) to complete each individual unit.
If you choose to sit the optional exam offered as a part of each unit, you will be awarded a Certificate of Achievement with a grade and percentage mark. This certificate may be used for evidence of achievement. If you choose to complete the progress tests only, you will receive an ungraded Certificate of Completion.
I'm not sure if this is exactly what you're looking for or not, but it's worth asking Melbourne or Monash if they'd accept this. If not, check out local TAFEs, Adult Education centres (like CAE) and places like Monash College.
Other than that, perhaps you can get a teacher who particularly likes you (or your principal if you can manage that) to write a letter of reference. Or if you could get someone from PWC to write something for you, that would be awesome (a bit of a stretch though).
This is a lot of bother, and you might not be accepted at either uni for Commerce in the end, but it's worth a try. Do you have anything better to do until uni starts? In any case, keep reporting on what's going on, it'll be interesting to see what happens.
If all that doesn't work, you can transfer after your second year or go to another uni (Deakin, for instance). There's still lots you can do.
EDIT: fixed link (hopefully)