Submissions can be emailed to GCSB.Bill@parliament.govt.nz. If you wish to appear before the committee, state this clearly and provide a name, daytime phone number, and email address. Submissions will generally be made public. The committee is required to report to the House on this bill by 26 July 2013.
No, they don't provide a postal address - so if you want to send hardcopy, you're shit out of luck.
The bill allows a massive expansion of GCSB powers and permits widespread spying on New Zealanders. As its mockery of a Regulatory Impact Statement shows, these powers are poorly justified. Please submit in opposition to this bill.