I've been in Famicase for a couple years, and even though the spirit of the thing is to make nonexistent games, I've been having fun using it as a proving ground for my cart dreams of my actual games.
Because of that, I've always asked other artists whether their carts were okay to use for AGBIC. I recommend you do the same, and if they have any restrictions, post them here so other folks know.
If anyone needs help finding/communicating with an artist, I know a bit of Japanese and would be happy to help.
For example: all three of these are games in progress. But you can totally still take inspiration from the carts, run with the style and the idea, but the name and such might actually be in use, so be conscientious :D