obtener todas las llaves foraneas de una tabla

SELECT f.name AS ForeignKey,
OBJECT_NAME(f.parent_object_id) AS TableName,
COL_NAME(fc.parent_object_id,
fc.parent_column_id) AS ColumnName,
OBJECT_NAME (f.referenced_object_id) AS ReferenceTableName,
COL_NAME(fc.referenced_object_id,
fc.referenced_column_id) AS ReferenceColumnName
FROM sys.foreign_keys AS f
INNER JOIN sys.foreign_key_columns AS fc
ON f.OBJECT_ID = fc.constraint_object_id
where OBJECT_NAME(f.parent_object_id) =('TablaAbuscar')
go

y despues para generar el script final debería ser así
alter table 'table name' WITH CHECK ADD CONSTRAINT 'foreign key' FOREIGN KEY 'columnname'
references 'ReferenceTableName'('referenceColumnName')