<p>I want to read all items of a feed in C#. The solutions I've found are only for the latest items like just the last 10 days.</p>

<p>Anybody has a good solution for this? </p>

Libraries for reading feeds typically read all the data in the feed, but feeds typically only contain recent data - you need a source of data that includes older items, not a better library for reading the data you have.
Most entities publish feeds to allow people to track when new content is published, not to make all their data available in a more convenient machine readable format. For this purpose, publishing recent data only makes sense as it saves on bandwidth.