If you are after a simple graphical diagram, you can find UML models under this Lyo-Docs
repo. you can find the source .emx files, as well as .png snapshots under the folder "OSLC-V2/images/".
I you are developing OSLC applications, you might want to consider the modelling tool Lyo Designer.
There, you can find a graphical model of the OSLC Core and Domain concepts. The models are based on a OSLC-specific modelling language. Lyo Designer allows you define/extend your own models, from which you can generate an OSLC application, based on the Eclipse Lyo SDK.
I here assume you are aware of the java class implementations of the OSLC Core concepts in Eclipse Lyo. There is also an implementation of the domain specifications.