This is a list of
Singer Sewing Machine cabinets with photos. The cabinets for the 201, 15-91, 66, 400, 500, 600 and 700 series are standard Singer Cabinets. The 99 is a smaller machine, as is the 221. Those cabinets are rare, though. Do not buy a Sears/Kenmore cabinet, as they are not the standard you are looking for.
As JoeJr. noted, the empty cabinets are widely available.
bk