Try this guy. www.boatbrochure.com
He may well have an original brochure and maybe an owners manual.
It also depends on which Islander 34 you have. The first version I'm not sure about. May well have been developed in house and based on one of the original Joe McGlasson boats.
If it's the second version, you can go to Robert Perry directly www.perryboat.com
I think he sells copies of all his original designs.
Let me know how you make out.
I am looking for original blueprints for the Islander 34. Any suggestions?