Sorangium cellulosum grows (slowly) on the media described in: Jaoua, S., Neff, S. & Schupp, T. (1992). Transfer of mobilizable plasmids to Sorangium cellulosum and evidence for their integration into the chromosome. Plasmid 28, 157–165.
For identification you could use characteristic chromosomal sequences, analyzed by PCR. The complete genomic sequence is published. This is easier than using characteristics of developmental stages.
For morphological and other characteristic properties of this bacterium, you may look into "Bergey's Manual of Systematic Bacteriology". Look for Sorangium and for Polyangium, There is, however, no culture of the type strain available. The important expert/literature is Reichenbach (around 2002; the original description goes back the 1930s).