There are a number of places you could try to have an antique sofa repaired. You may want to try Furniture Media, Workers in Wood, or Furniture Fixer, which are all able to deal with antiques.
There is no alternative to surgical repair. Risk of infection and damage to the spine and brain is high with an opening to the spine, so surgery is necessary to close the opening and drain the excess...
NO, antique dealers sell antiques. If you need repairs you can take them to a specialty repair person who specializes in antiques and can make repairs while maintaining the integrity of your piece.