How about this
Long objectGuid = 123456789L;
IMendixObject imo = Core.retreiveId(getContext(), Core.createMendixIdentifier​(objectGuid));
Something like this?
https://apidocs.rnd.mendix.com/8/runtime/com/mendix/core/Core.html#retrieveId(com.mendix.systemwideinterfaces.core.IContext,com.mendix.systemwideinterfaces.core.IMendixIdentifier)
You can use getGUID from CommunityCommons