need help to find airfoil coordinates

That's not a problem. When you import coordinate data like that into solidworks it generates the curve/spline from the first point to the last data point. Just use a second spline and make it tangent to both ends. Even drawing a straight line between the two points is probably enough. When you go to make it G code is going to chop it up into line or arc segments anyway so don't feel too bad about just filling the gap. If that's the published coordinate set you're working is what it is. Most airfoils are equation driven and you can A: program the two equations into solidworks... or B: in whatever program you're using just increase the number of segments to make the gap smaller. Just fill the gap and move on.

Alternatively, edit the coordinate file so it starts at the trailing edge and add that same coordinate where it ends at the trailing edge. There is little need for decent smoothing at the trailing edge and there is need for a smooth surface at the leading edge; put the discontinuity where it does the least damage.

or just a straight line !? though obviously a cubic spline would fit better.

Is this a very old airfoil section ? a google of "c3x airfoil" gave lots of hits ...

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.