Blog Posting is where you write content of about 400 words and can have your link in the content. Some Blog Posting sites are Wordpress, Tumblr, Blogger, etc. Blog Commenting is when you have to comment or express your views on a particular post and try to get a link from it.
Hi Main difference is in case of blog posting we submit a new content on blog and in case of blog commenting we make the comment on post which is done by any other user. Hope you understood.
I don't have the sites, but I can give you a method to find sites.....Type in Google.. "Login or Register to post comment" + keyword This should help you find a lot of sites....