You shouldn't have any problems finding one of the original 80s one. As with the standard 20" Burners, the Mini's also had Mk1 and Mk2 models, these are recognised with the Mk1's having the gusset between the 2 main frame tubes, and the Mk2's having the oval tubing, and no gusset.
There were Raleigh Burners made more recently, but they just carry and share the name, they're made by the firm that bought Raleigh (Tailwanese probably), nothing whatsoever to do with the iconic 1980's Burners made in Nottingham.