Sodium concentration during action potential generation
Below is a schoolbook example of the membrane potential combined with the individual conductivities of Na+ and K+ during an action potential (AP) (Fig. 1); 


Fig. 1. Membrane potential and conductivities of the two most important ions in AP generation. source: Physiology Web 

And in Fig. 2 is an example of the currents of Na+ and K+ during an action potential (AP) (Fig. 1). Note that K+ stays high due to amanipulation of ion concetrations.

 
Fig. 2. Sodium and potassium currents during AP generation. 

However, you ask about the concentrations of Na+ in the cell. As far as I know, this has not been investigated directly. Intracellular Ca2+ concentrations, for example, can be imaged with various imaging techniques, but absolute Na+ and K+ concentrations have to be measured with intracellular electrodes. So while the conductivities and the currents are depicted quite clearly in the above figures, they do not show the absolute concentrations of Na+ or K+ and I doubt it can be found anywhere in the literature. It can of course be mathematically deduced, by calculating the number of ions entering the cell using the Nernst equation and correcting that for the background effect of the sodium-potassium pump and other factors that alter Na+ concentration in the cell (protein transporters and what not). It will at least give an approximation of [Na+]i.