GDRI

Most Atarisoft games were developed by outside contractors except for ColecoVision and Intellivision games. (Atari actually hired former Mattel programmers to work on the Intellivision and was promptly sued by Mattel.)

One of the contractors was International Computer Group, which was mostly known as an agency representing video game publishers and developers. ICG did its manufacturing in Hong Kong. The inside of the screw holes allegedly say "ICG."

Most Atarisoft games were made in the USA, so that isn't too helpful, but some of them were made in Hong Kong.

They were mostly, probably all, developed by Syndein Systems, which was apparently a subcontractor to ICG. (ICG didn't seem to do any internal development.)

C64 Atarisoft games developed by K-Byte use the same cartridge shell as games published by CBS Software, a different shell from what the few other C64 Atarisoft games use. This would suggest these cartridges were made by K-Byte, which had its own manufacturing facility.