The problem is compacted by the fact that we're not exactly sure where or how the turkey will show up. Some users on the game's official forums state that they've found the turkey sitting at the very beginning of Beaver Valley, where you first started out, and that you don't have to draw a turkey out manually with your Hunter. For those that don't have a turkey sitting there, you may feel obligated, or at least desperate enough to spend dozens (or worse - hundreds) of Rations chopping down trees, clearing debris, harvesting berries and other tasks, just to try and bring a turkey out. Even then, if you're lucky enough to get a turkey onto your trail in this manner, the blue exclamation point doesn't seem to appear then either!
The only workaround for this issue as of this writing is to write Zynga Customer Support, or use their Live Chat service on their website. You can't even pay Horseshoes to skip the mission and finally escape from Beaver Valley, as the Horseshoe option simply isn't available. It's either contact Zynga Customer Support, or wait until the game can be fixed. When will that happen? Your guess is as good as mine. Good luck finding a turkey in your own game, pioneers - I think we'll all need it.
Have you been able to complete the final hidden mission and leave Beaver Valley, or are you still trying to find a turkey / blue exclamation point to receive it? Was Zynga's Customer Support team able to help you? Sound off in the comments.