Might be clutch not disengaging all the way or a transmission problem.

Does it engage all gears ok with the engine off? If so possibly clutch, if not probably transmission related.

If it is only the clutch, check fluid and bleed. Check slave cylinder is activating correctly and not leaking. If all ok take the transmission off and inspect.

From your description with not being able to find neutral it does sound like a transmission/shift fork related problem.