When I want to find a \"Big\" Web service (WS-*/WSDL based) of required functionality I can simply google for \".... filetype:wsdl\" because Google indexes also WSDL definit
SoapUI now can discover the REST services. It works as a proxy, writing down all requests/responses that pass through. Having requests and responses SoapUI recreates descriptions/definitions of the services. Now the definitions can be stored in WADL and WSDL formats (as WSDL and XML-Schema in XML world). It also can be stored in Swagger format. I prefer Swagger. Swagger can be stored in SwaggerHub right from SoapUI, which is like GitHub for source code. SwaggerHub is one of many API management systems.