I guess you want something along the lines of
julia> Iterators.product(A[:, 1], A[:, 2]) |> collect
4×4 Matrix{Tuple{Int64, Int64}}:
(1, 5) (1, 6) (1, 7) (1, 8)
(2, 5) (2, 6) (2, 7) (2, 8)
(3, 5) (3, 6) (3, 7) (3, 8)
(4, 5) (4, 6) (4, 7) (4, 8)
Tweak shape etc. as needed.