YOu will need to go to a Ranger Boat dealer. You can also order right from Ranger but you will have to call them as that item is not listed online ar in there catalogs.
I’m not sure what they cost but I assure you whatever the cost it’s worth it. I spend many hours a year fishing out of my friends 619 and it saves my back while pitching and jigging. It definetly gets in the way while trolling cranks but can be removed easily.
I believe they are in the $500-600 range. My boat came with one, but I pulled it out and sold it on C list. I was surprised when I sold it in about a half hour. I thought I would have that thing sitting in the corner forever.