These are the contact details for the fabric shop in Otahuhu that has lots of cheap linen ($3-6 a metre) as well as cottons and other random stuff. It pays to phone first and check if he's open, as he's been pretty sporadic this year.
Tel: 270 4948
16 Hall Avenue
Open Monday-Friday 10am-5pm
Closed Sundays, and when he's called on business to Hong Kong