It may be a C5 connector...
http://www.leadsdirect.co.uk/technical/iec.html
http://www.amazon.co.uk/Clover-Leaf-Notebook-Power-Cable/dp/B000YHZV1M/ref=sr_1_1?ie=UTF8&qid=1259145335&sr=8-1-fkmr2
Other people have looked for this part on here - if it's not a C5 connector and just specific to Sona then it may be possible for you to remove the fixed receptacle in the machine and replace it with something more standard... Free end = odd number & fixed = even
IEC C5/C6
IEC C13/C14
IEC C15/C16
Good luck...
Peccavi
November 2009