Upvote:5
This question has a false premise: it is not necessary to present your decision letter at the border.
However, it is possible nonetheless to get a copy of the decision letter for any UK visa application. You should make a 'specific' subject access request to the Home Office.
If you have a physical copy of the decision letter already, scanning it will be much easier and faster than making this request, which may take weeks or even months to process.