Hello Prabhaharan,
One thing is not clear here. When you have successfully modeled your entity to handle media content in service builder and you have also put your code in Create_Stream and your able to upload Media content , why you want to enhance your model now ?
There is no need to enhance your model here or add custom method here. Its not necessary at all.
You just have to put code in Get_Stream and Read the media content with the URL which i have shared in previous mail & sent back the response correctly with mime type and value. That is it . You should be able to Read content.
Please note that when you are able to create you should be able to read as well with the same entity. No adding custom method for content type and enhancing model needed here.
Regards,
Ashwin