Yup! Old school stuff, this type of equipment is all still available, an old bike shop will have it in the back. A community bike shop will have bins of the stuff used. The post is most likely 7/8” (22.3mm I think ) the old standard off your Dad’s Raleigh. The seat is a cruiser design.
Trek has a seat like that in its Electra line up, I have them on both of my wife’s bikes, she loves them. It’s available as an accessory part.