Can anyone recommend a tour company from Marrakesh to the Sahara? I will be travelling alone in March and would like to join up with a small group. Thank you for any information

You could try the trip finder @ Wanderlust Magazine - see www.wanderlust.co.uk/planatrip/
Not sure about dates of trips but look @ Exodus - www.exodus.co.uk or Explore - www.explore.co.uk
From Marrakech see Hotel Ali, near Djeema el Fna.
But I think for the Sahara you'll have to travel north. Most of the overnights (or longer) leave from some place that begins with an 'M'. (Sorry, my memory isn't so good on place names.)
Or much further south - about 12 hours by bus.
But better to ask this question on the Moroccan branch, in Africa (manin board, above).