Assembly.GetExecutingAssembly doesn't exist in PCL

In general, you should use something like typeof(MyType).GetTypeInfo().Assembly instead of Assembly.GetExecutingAssembly(). GetExecutingAssembly has to basically examine the call stack to figure out what method is calling it and then look up the corresponding assembly. This could break if methods are ever inlined across assembly boundaries, which is why the GetExecutingAssembly method isn't in the "new" reflection surface area which Profile 78 (as well as .NET for Windows Store apps) uses.

The separation runs indeed deep and quite meticulously within the PCL.

It is crucial here to understand that the Portable Class Library as a platform profile doesn't exist. The running application will not incur the same restrictions as the compiler does, upon compiling your PLC project.

Here is one way to break through the barrier:

using System;
...
try {
    var getExecutingAssembly = typeof(Assembly).GetRuntimeMethods()
                                .Where(m => m.Name.Equals("GetExecutingAssembly"))
                                .FirstOrDefault();
    var assemblies = getExecutingAssembly.Invoke(null, null);
} catch(Exception exc){
   ... try something else
} finally{
   ... time for some alternative 
}

This approach will only yield you the accessible assemblies within the sandboxed assembly environment. But it gives you a starting point on how to access the "stuff" you are not supposed to.