The recommended retainer is P4452032
Mopar Performance P4452032 Mopar Performance Valve Spring Retainers | Summit Racing
Kind of spendy but not discontinued. I think the price is due to the material. This same retainer is recommended for the 2.2/2.5 and people use the standard ones without issues.
Note that there are discrepancies on the angle of the keepers. The MP catalog I am looking at says those retainers use 8 degree keepers, but the Summit listing says 7 degree. Just an FYI.
Lastly, I guess these are the same springs the 380hp crate motor shipped with. If that gives any idea of the application.