Depending on the circumstances, you either need to follow the procedure for getting your licence back after disqualification or the procedure for when your licence has simply been lost. In practice, they're the
same procedure:
If you want to get your licence back after disqualification (and DVLA haven't sent you any relevant paperwork), you should fill in
form D1 (from a Post Office):
http://www.direct.gov.uk/prod_consum_dg/idcplg ?IdcService=SS_GET_PAGE&siteId=en&ssTargetNode Id=285&ssDocName=DG_4022491
If you want to get a new licence because your original licence has been 'lost' (i.e. it's stuck in a dusty cupboard in a courtroom somewhere), you also need to fill in form D1:
http://www.direct.gov.uk/prod_consum_dg/idcplg ?IdcService=SS_GET_PAGE&siteId=en&ssTargetNode Id=283&ssDocName=DG_4022085
So, fill in form D1 and then write a letter, to go with it, explaining your unusual circumstances. (If there are any awkward questions on the form, simply write 'Please refer to accompanying letter').
Chris