Do you get AUTOMATICALLY a scout or a sharpshooter in the first sector?
Yes and no. You DO automatically get them but not in sector 1. They are in Sectors 2 and 3, respectively.
Those specialist cards are only available in the British deck.
Each nation has the exact same deck of Specialist cards. You should have 4 each of the Scout and Sharpshooter in each player color.
Do this mean that other forces can not participate in this scenario?
No, as mentioned above, they all have the specialists.
Can specialist cards be traded?
No, specialists cannot be traded unless something specifically says so (like the Messenger).