you cannot currently legally purchase game packs for the ultracade.
the original maker of the ultracade system did not obtain permission to use the intellectual property of the game makers to use them with the system. before the companies found out, he sold the business to Global VR, telling them that he had permission and paid licencing to use them. Global VR ended up paying a whole whack of money to the original game makers for stealing their games...even though they didn't do it.
in a nutshell, any packs our there are illegal to sell, because there is no permission from the original game makers to use it.
Global VR obtained legal use of some games, and have since re-released the system under a different name.
http://www.globalvr.com/products_gac.html They will not support the ultracade, they will not talk to you about it.
BUT you are in luck in another sense. The IO board used in the ultracade is simply pretending to be a keyboard. you can build a computer, install MAME and have whichever games you wish. all the controls are just button presses on a keyboard.