There are relatively few jobs in Madrid that explicitly look for Gwt competency: At the present moment, Jobspotting features 6 jobs for 5 distinct companies. Subsections include most dominantly Java and .Net. Hibernate, Jpa and Apache Struts are important to know when applying for jobs in this area.
If you're at the present moment seeking experienced positions, sign up to Jobspotting now. Corporations are looking for professional candidates like you. Among the host of companies on Jobspotting, there aren't currently any startups hiring for Gwt. Why not have a look at jobs in another country to compare and contrast opportunities. Just use the Explore tab.