Actually ...Async stuff is not related to the way server is defined - ie is it CodeFirst or RODL-based one.
The interface file generated client-side contains ..Async methods when the code generator assumes that the target platform supports async/await.
So if your client for the RODL-based server is targeted at .NET FX 4.5+ or other platform that supports async/await then you can do one of the following:
* Use the same 'Connect To The Remoting SDK Server' command as you would do for the CF server client
* Open the RODL in the Service Builder, go to Code Gen -> Language -> Interface and take the code generaed (by default it will contain the ...Async methods)