Get the Annotations of Enum Fields Follow

Try getEnumConstants() instead of getFields(). This is not MPS-specific, by the way, it's just Java reflection.

Actually, scratch that. Your code is correct, but the annotations themselves need to be annotated with @Retention(RetentionPolicy.RUNTIME)

Sergej is certainly correct, but it seems there is a more "MPS" way to do this, that isn't an enum-with-annotations.

I would think about structuring the project this way:

concept MeasurementType extends BaseConcept
                        implements IValidIdentifier
   ...

   children:
     valueType: Type[1]        

concept MeasurementTypes
   ...

   children:
      types: MeasurementType[0..n]

Then depending on where you need that information, you could create a template that creates an enum from those concepts, or create a subconcept of Type which references a MeasurementType, and replaces itself with the valueType.