PI API is not supported under vCampus but you can download it from OSIsoft TechSupport website. You should see a download called "PI API Install Kit for UNIX AIX (32-bit)". In case you don't, please contact OSIsoft TechSupport in order to find out the reason.
Hope this helps you!
vCampus is the place to ask questions related to application development. Hence your question makes me wonder why you are asking for PI API for UNIX AIX.
As Marcos said, PI API development isn't supported at vCampus. Because vCampus is the place for PI geeks who like to develop applications on top of the PI System, the conclusion is that we (OSIsoft) do not support development against PI API at all.
Further Marcos reply indicates, seeing the PI API for UNIX AIX setup kit at Technical Support Download Center would be common. Indeed the opposite is the case. This download is available to very few customers only. To my knowledge these customers bought PI API for UNIX AIX long time ago, when developing against PI API was supported. This said, PI API for UNIX AIX exists because of legacy reasons.
Can you please explain the background of your question?