Work experience when you're young. How would you do it?

Hi, I'm currently 17 and very interesting investment banking finishing lots of work experience in the public sector for Australia in accounting and finance this week. (DHS, Welfare payments, medical welfare) and found it pretty interesting, but not close enough to what I am interested in.

I got the chance to meet someone working in Merchant banking, he was pretty awesome and warned me about the hours and the time put into the job.

Being said, I now want to step up and get some work experience in some form of investment banking role, or anything close to it. I don't think and bank or firm will take me seriously when I ask for work experience (I have tried) and I believe it's still possible to secure some kind of exception.

If you were in my shoes, and direct answers only please; how would you get work experience at a firm?

- There are lots of firm buildings local to where I live, but I don't think I can walk in there; and all my emails will be ignored.
- I could make some cold calls, but because I'm both young and am interested in something almost none of them provide, also likely to be ignored.
- If I was going to cold call, or email and try reach out as much as possible... how would you do it (if you think this is the best option) ?