I noticed that, for some reason, there's no listing for the DS cheat saves device on store.madcatz.com. Is it not being made anymore?

Unless Madcatz made any specific announcement concerning the sales of that product the staff can't confirm anything based solely on the fact that it's not currently on the main online store. If it's not available through there then it should be available through other retailers that stock the product as long as the company is still shipping them.