You may refer the method used here to find the neighbouring values of an element in a matrix. To find the locations of elements in a vector, you may refer the find function.
You may also refer the example below that finds neighbouring cells for values greater than 50. The code can be modified to find neighbours greater than 50 as well.
>> A = [3;4;8;6;51;5;8;65;9]; % size - 9x1
>> M = zeros(size(A.'));
>> C = find(A>50);
>> M(1,C) = 1;
>> Neighbours = A(conv2(M,[1,1,1;1,0,1;1,1,1],'same')>0)
Neighbours =
6
5
8
9
