OK, I'll assume that we've established that there's no transformer. In which case, the connector which goes into the sewing machine is likely to be one of three types:
Firstly, it could be a 'figure of eight' connector. This is probably unlikely because there are only 2 pins and it's likely that a sewing machine will have an earth pin as well. But if you can see that the hole which the lead plugs into represents a figure of 8, then this is the lead you require (�3.99):
http://www.maplin.co.uk/module.aspx?TabID=1&criteria =mains%20lead&ModuleNo=1168&doy=19m1
If, however, that hole is a 'cloverleaf' shape, then you require this lead (�3.99):
http://www.maplin.co.uk/module.aspx?TabID=1&criteria =mains%20lead&ModuleNo=29240&doy=19m1
If the shape of the hole is the same as the one in an electric kettle (or on the back of your PC) then you need an IEC lead (�3.99, �4.99 or �5.99 depending upon length):
http://www.maplin.co.uk/module.aspx?TabID=1&criteria =IEC%20mains%20lead&ModuleNo=1176&doy=20m1
(NB: If this is the correct type of lead, and you've got an urgent sewing job, you can simply borrow the lead from your PC or kettle).
Having got all of the transformer-less leads out of the way, I'll return to the possibility of a power supply using a transformer. If your sewing machine uses this type of lead then it should still be possible to get a replacement item from Maplin Electronics but I'd advise taking your sewing machine into one of their shops so