There seem to be 3 possible sources of blowers in Australia:
Flea Markets
Good fans are not commonly found at flea markets, but it does happen. It may
be necessary to buy a complete piece of equipment, just for the fan!
If you stumble across one of the old English fans made by Woods, grab it.
They need occasional lubrication but are excellent, and will give long
service.
American Dayton Blowers
Dayton fans seem to be used in most American equipment. They are
available in 230-volt as well as 115-volt models.
Dayton fans are supplied by Grainger Industrial Supply, a wholesaler, but
you can buy direct by setting up an account even for a single purchase, or
by finding someone who already has an account.
Construction uses rolled steel, giving a flange which is not as flat as a
diecast type, and possibly slightly noisier operation.
My own experience has been that packaging was not adequate, the fan being
more or less loose in a box; the flange was slightly bent on receipt, but
was easily straightened.
The model I bought was a 2C915, rated at 140 CFM (cubic feet per
minute), which translates to 238 cubic metres per hour (m3/h). This is the
volume of air available in the open with no back pressure.
The most suitable current model seems to be the 1TDP6, rated at 133 CFM (or
226 m3/h).
Price is under US$100, to which you must add freight costs (US$56 in late
2007), so in November 2008 you are looking at some A$230 all up.
German EBM-papst Blowers
EBM fans use diecast aluminium for the scroll and flange, and are highly
regarded.
The most suitable models seems to be the G2E108 and the G2E120.
The G2E108 is rated at 91 CFM (155 m3/h) with no back pressure, and the
G2E120 at 150CFM (255 m3/h), so the G2E120 is preferred.
EBM fans are available in Australia through both Farnell and RS Components,
with Farnell being rather cheaper at November 2008. Prices are still well
over $300 ex GST!
It may be possible to buy directly from overseas - I don't know.