Immediate family members of a service member who died in the line of duty can get the Missouri Some Gave All Gold Star license plate. You have to make a $25 donation to the Missouri Department of Veterans of Foreign Wars, which then issues the Emblem Use Authorization Statement your application needs.
Contact the Missouri VFW to make the $25 donation and get your Emblem Use Authorization Statement, then submit it with the Application for Missouri Military Personalized License Plates, Form 4601, to the Motor Vehicle Bureau.
The Emblem Use Authorization Statement from the Missouri VFW, documentation of the service member's line of duty death, and proof of your relationship to them.