I got one from ItalianBenz, I think he said it was installed factory on his 500E, dunno the brand name, maybe Benz Key, according to this post
http://www.peachparts.com/shopforum/showthread.php?t=99168&highlight=keyless , might have to ask him for more info on it. But it just went right into the trunk unit, and it works pretty easy, one click locks, two arms the alarm, I think... Maybe the second button arms it. Anway, I think my system is the same as yours its a 92 300CE, probably a lot closer anyway, than a 95. I have searched for the unit I have, on the internet, never called the dealership, and its not in the service CD, and found nothing about it, so i'm sorry I cant be of more actual help, but maybe something you can find more on than me. But apparently it does exist.