Charles Daly doesn't make any guns, they have other companies build the guns and then put their name on it.
There have been so many, you will have to identify the make model, who made it and if the company produced the same gun as another make/model.
Then contact Charles Daly to see if they offer or offered one for that gun. Either they will be able to sell you one, or let you know if they ever did.
If they are not able to sell you one, then check the various auction sites. The final option is to have a gunsmith add rifle sights to the barrel, but that won't help you with the rifled part.
When it is all said and done, I think that you will spend about the same amount buying a 20ga H&R ultra or Tracker II.
As far as accuracy, a rifled barrel will be more accurate, and have more downrange energy. But slugs for rifled barrels will cost more. Effective range is more dependant on shooter skill.
Feel free to stick around and read some of the many topics around 20ga slugs.