Using Windows Server 2008 R2.
I know that there are extensionattributes 1 - 15 available but I can't figure out a way to view / access them?
I have used both ADSI Edit and ADUC but neither seems to show them.
They're visible in ADSIEdit, or the Attribute Editor tab in ADUC with the advanced features enabled.
It sounds like you don't have the MS Exchange schema extensions installed; that's what installs those attributes into your schema.