I immediately viewed the blog when I first saw this posted. i viewed it in Firefox 3.5.7 and in IE 7 and in IE8. I'm not able to access the computer with Opera installed right now but in the three browser I used I could see all the widgets very clearly. Consequently, I assumed what the OP meant was that viewers would be unlikely to look for the post in question by searching in the Archives.
The blog is in Polish but I can read it. The widget titles are:
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I do not know what "this means no widgets were used" means.
Some posts have categories/tags and some do not. The OP has not provided the link to the post. in question. The OP has not stated that there is new information intended to be included in the existing indexed post which is in the SERPs and is resulting in traffic from search engines.
The OP has said: "I've tried unarchiving the post, but this hasn't worked very well."
I do not know of anyway to "unarchive" a post. Posts are immediately and automatically added to dynamic pages like Archives and Categories after we publish them. The only way I know of removing a post from the Archives display and display on other dynamic pages is to delete the post, which will produce a broken link and a 404 message for every reader who uses a search engine and tries to find it as it has already been indexed.
The OP says: " I'd like to create a page with the same content, and then redirect google traffic from the post to the new page url. How is this possible? "
Let's break that down into two parts.
Part 1 " I'd like to create a page with the same content".
That's easy enough to do. There is no automatic way to repost content from a post to a static page; the solution is copy and paste. However, unless the post is then deleted it will lead to duplicate content issues.
Part 2 "and then redirect google traffic from the post to the new page url."
Static pages cannot have categories and tags assigned to them and have they have very little Google juice. There is no way to redirect search engine traffic to the new static page, unless one does that from the post itself, provided it hasn't been deleted. And if it hasn't been deleted then then we have come full circle back to the duplicate content issue.
Setting aside the redirect search engine traffic concept, any readers who so arrive on the site can be directed to the post itself as raincoaster has suggested ie. by using a text widget at the top of the sidebar. Well, that brings us back to the OP's belief that visitors cannot view the widgets in the sidebar.