Simple harmonic motion is a system whereby the total energy of the oscillation is constant and therefore the wave would have a constant amplitude. Doesn't that mean for a simple to display s.h.m it would have to be 100% efficent? Is this one of those things where its not possible to reach the ideal?

Yes, true SHM would be 100% efficient, but in general what is observed is damped SHM, where a damping term based on the velocity of the oscillator is introduced. I assume you were talking about a simple pendulum above which actually does not display SHM either, it only approximates it for small displacements.

But could you say a vibrating machine for example would show SHM if you ignored friction. Obviously this would be impossible as there would be friction and at least limited damping but ignoring that. Or would it have to be a pendulum.

Yes, SHM is observed in hundreds of examples, and is a generalisation of the more general travelling wave equation, which is probably the most common phenomenon in physics.

what about a lagrange point? an object in space at the lagrange point wobbles back and forth almost non-stop, right? what friction slows that wobble?

If it's a lagrange point, then it's going to collect "dust"- that causes friction.