I'll upload one of my drawings that I used 0% reference, that came from my imagination
Trust me, It is my goal to attend life drawing classes, I have also searched the web for real life photos of people of similar poses I desire. I know a DC comic artist named Alex Ross that photographs live models with costumes.
Posemaniacs helps me sometimes, but only when i practice gesture drawing, the poses in that site are not exactly what I look for. I draw in shapes like using ovals for upper legs, upper arms,big inclined oval for torso,oval for head,squares for hands,rounded cones for lower legs,and fore arms.
most of the times when it comes to drawing from imagination is having trouble starting, I get puzzled when it comes to the shape of the torso which I try to start from because it's the core of the figure and it gives you an idea of where the other limbs will go. I tried using a sphere for a torso but it doesn't work much, the oval is kind of hard in all angles, I've tried using a triangle but then again in a bird's eye view or other angles I need the shape to be 3D.