I live in Brisbane, Australia and want to import (I'm assuming the
substance isn't made locally in Australia) bulk quantities of xylitol
at wholesale prices, to repackage and sell here by mail order. Who are
the main wholesale suppliers?

Dear karon,

Xylitol suppliers are not easy to locate. However, I managed to find
these three British chemicals manufacturers who offer direct selling
of xylitol in wholesale quantities:

VWR International Ltd.
Customer Service Centre
Sales Office and Order Processing 
Hunter Boulevard
Magna Park
Lutterworth
Leicestershire
LE17 4XN
United Kingdom
Phone: +44(0)1455 558600 
Fax: +44(0)1455 558586
E-Mail: uk.sales@uk.vwr.com
Website: http://uk.vwr.com/

Molekula Ltd.
Technology Road
Poole
Dorset
BH17 7DA
United Kingdom
Phone: +44(0)1202 330066
Fax: +44(0)1202 330055
E-Mail: info@molekula.co.uk
Website: http://cgi.www.molekula.co.uk/

Forum Products Ltd.
Forum Food Division
41-51 Brighton Road
Redhill
Surrey
RH1 6YS
United Kingdom
Phone: +44(0)1737 773711
Fax: +44(0)1737 779544
Website: http://www.forum.co.uk/

Sources:

Chemical Industries Association: Xylitol
http://www.sourcerer.co.uk/asp/ChemicalDetails.asp?txtChemid=001012000

Search terms used:
"xylitol manufacturers"
://www.google.de/search?q=%22xylitol+manufacturers%22&ie=UTF-8&oe=UTF-8&hl=de&meta=

Hope this helps!
Regards,
Scriptor