Forgot to update my original enquiry here. I got a replacement battery for $149.00 from Salton NZ and it's working great. Excellent service, the price included delivery within 1 day (within Auckland, admittedly)!

They also sell other parts (prices correct on 10/2/2010):
MAIN BRISTLE BRUSH WITH BRUSH COUPLING (11237) $21.00
MAIN BEATER BRUSH - RUBBER (11238) $19.00
SIDE BRUSH WITH SCREW (11239) $12.00

Contact details:

Candice Brackenridge
Salton NZ Ltd
DDI: 09 920 2573
Fax: 09 920 2574
Email: candiceb@salton.co.nz