Allwood Sails in Sydney sells Harken 16mm blocks:

HK404  16 mm Air Block with O ring for $17.5
HK405  16 mm Air Block with becket for $20
HK406  16 mm double Air Block for $37.00
HK407  16 mm double Air Block with becket for $40.50
HK408  16 mm triple Air Block for $52
HK409  16 mm triple Air Block with becket for $55
HK416  16mm cheek Air Block for $20.5
HK417  16mm swivel Air Block for $32
HK421  16mm Exit Block for $49
HK376  16mm forkhead Block for $25.5

Click on the image below to go to the Harken catalogue: