In Gmail under Settings>>Filters create a filter that will select all of the 100 emails you want to forward. You may have to play around with the some to get it right, but you can use the TEST SEARCH button to make sure you have the right messages selected. Click on NEXT STEP.
Put the address you want to forward to in the "FORWARD IT TO" box.
Once you have the filter right check the "ALSO APPLY FILTER TO... CONVERSATIONS BELOW" then click on CREATE FILTER to apply the action to the selected conversations. You may want to delete the filter after you are done if you don't want to keep forwarding.