Around here most of the op shops have old gents tweed jackets, though it takes a few different stops before you're likely to find something that fits. Sometimes they do have complete jacket/pant combos, but they're pretty rare to find something in your size. The next step is suss out some vintage clothing places, this is the kind of place you're much more likely to find the vests. Not sure if there's any up your way, but there'd be some great ones in and around Brisbane.
Other things to consider:
* If your lady (or your mum) is handy with a sewing machine, some full length pants can get taken up for that plus 4 look.
* Myers (down here anyway) have some woolen vests in their menswear section.
* Some modern 3/4 shorts can pull off a vintage vibe if teamed with the right stuff. I've got some beige ones with a light coloured pinstripe, and with a plain white t shirt and some suspenders they look pretty cool.
* Clip on suspenders can be picked up on ebay pretty cheap and totally sell the vintage vibe, plus you can get away without wearing a jacket which is much better for your climate!
Even jeans when teamed with a vest and a regular business shirt and a tie can get the right vibe
