In blogger, you cannot redirect specific page or post to an external domain till now. I have seen many bloggers for searching for this. After a few minutes of work, I have made 3 simple lines of code that can help you in this case. I used simple meta tag redirection for it.
Follow The Bellow Steps to Redirect Specific Page In Blogger.
1.Copy The below-given code.
<b:if cond='data:blog.url == "SOURCE-URL"'> <meta content='0; url=http://www.External-Domain.com/ ' http-equiv='refresh'/> </b:if>
2. Now Paste The Above Code In Meta Section Of your Template.(Don’t Forget To take backup of your Template before this.)
3. Now Just Change Source-URL with the URL of your blog which you want to redirect and http://www.External-Domain.com/ with the site you redirect that page. Don’t forget to use http://. Now save your Template and try.
With above method, you can easily redirect specific page or post to the external site easily. According to me, blogger is a very awesome blogging platform we just need a little bit knowledge of HTML to make important changes.