You are referring to a DDS green-screen keyword, but you posted this as a "rich display" issue. Rich Displays do not use green-screen keywords.
If you mean that you are having this problem in a 5250 display rendered by Genie, then my guess would be that it is a feature of 5250 that wasn't added to Genie. Most Genie users will use subfile detection to convert their subfiles into web-based grids, so not many people use a 5250 scrollbar. But, if that's something you want, you could consider sending a feature request to profound logic by e-mailing
support@profoundlogic.com to see if it could be added. (It might be worth noting that many green-screen 5250 emulators, and several actual 5250 terminals did not support *SCRBAR either. It was an optional enhancement that Client Access supported, but many others did not.)
If you do mean a Rich Display, then the SFLEND keyword, like all DDS keywords, is not used. Instead, you will need to set the scrollbar property of the grid widget. Rich Displays, of course, fully support a full scrollbar, like you would expect in a GUI application.