There are several data sets available pertaining to ecoregions and ecoregional assessments at The Nature Conservancy. If you have any questions please contact Jim Platt (firstname.lastname@example.org).
1) If you are looking to download spatial data delineating the The Nature Conservancy’s ecoregions and ecoregional assessments, they can be found at http://maps.tnc.org/gis_data.html. Scroll to the bottom to view or download this data.
2) If you just need a list of the ecoregions that TNC uses, you can find it at http://www.conservationgateway.org/Documents/ERlist120208.xls
3) Information about past ecoregional assessments
that The Nature Conservancy (and some of our partners) have conducted
can be accessed from the Ecoregional Assessment Status Tool (EAST): http://east.tnc.org. This includes the full reports from the assessments.
4) Information about the process of conducting ecoregional assessments can be found on the Conservation Gateway: http://www.conservationgateway.org/ConservationPlanning/SettingPriorities/EcoregionalAssessment/Pages/ecoregional-assessment.aspx