People have been asking this for years. It's very unlikely that anyone still has an unbuilt kit, let alone one they'd be willing to part with.
If you want a G-Boy, you'll have to aquire all the bits from Dustin's updated project here:
https://bitbuilt.net/forums/index.php?threads/g-boy-pcb-files.5054/#post-55947
It has the BOM, the files to 3D print the case, and the files to order modified custom PCBs to work with the new 4layertech boards. The result is virtually identical to the original kit, with the added bonus that the newer componets are easier to service.
There's also the Ashida, which is a much easier project for a first time builder.