Is it possible to find how the cross section of DNA looks using without computer simulations ? All pictures I find on the internet are mainly computer simulations.
Yes. We can use some specialist applications of electron microscopy to do this. This does rely on a computer to do some of the imaging (think very fancy camera).
There is an open access article at Science Advances that has images from transmission electron microscopy of DNA, specifically figures 1 and 3. Note: As mentioned by @timeskull figure 3 is a simulation of the HRTEM method that they used. Real HRTEM images are in figure 1.
Ref: Marini et al., 2015. The structure of DNA by direct imaging. Science Advances vol 1, issue 7.