Welcome to the Lounge

return source.Select(t => new 
                          {
                              Index = rand.Next(),
                              Value = t 
                          })
             .OrderBy(p => p.Index)
             .Select(p => p.Value);

return source.Select(item => new 
                          {
                              Index = randomiser.Next(),
                              Value = item
                          })
             .OrderBy(sortItem => sortItem.Index)
             .Select(sortItem => sortItem.Value);