No, unfortunately, there is no A4 HEMTT kit available yet. Trumpeter has shown an M1120A4 as part of their forthcoming US Iron Dome System kit. We’ll see if it is actually on an A4, or if it’s simply slapped onto their existing M1120A2 kit.
There is a 3D printed HEMTT A4 conversion set in the works by a member here, @CAD_user. It is looking good but will be pricey.
3D HEMTT A4 Conversion Parts in the Works - Armor/AFV / Modern - KitMaker Network
Or you could just build your own.
M978A4 HEMTT Fuel Truck (Former M983A4 build) - Armor/AFV / Modern - KitMaker Network