Where can I find trees preserved for hundreds of years?
Yes, this occurs fairly regularly in Alaska and British Columbia (and probably other places with low-elevation glaciers that interact with forested zones) where climactic oscillations have led to rapid advance and recession of glacial extent. 

In Glacier Bay, Alaska, for instance, there are a number of interglacial stumps (you can see a few sites marked on this map). These stumps represent a forest that was established in the ice-free interim period between the Last Glacial Maximum (10,000-15,000 ya) and the "Little Ice-Age" (~500 ya). Thus, these trees have been preserved under the ice for a few hundred years and have only been uncovered recently (&lt;100 ya). Many of the glaciers in Southeast Alaska are receding, so new stumps are being exposed every day.