How to paint an Eldar Crimson Hunter? 1/4

Where would I get plastic putty to fill the gaps? I would like some for my wraith knights and crimson hunter. does it work well on smaller models like wraith guard and dire avengers? if not what else would you recommend?

You may use it if you will have access to fill the surface when it's hard. I used Vallejo Plastic Putty, but I also like Humbrol Model Filler. For the crevaces with poor access I use good old green stuff