That's not much room... especially when you consider that you need room to get the top off and into the neck for cleaning.
Several high end manufacturers make short skimmers, but they are very expensive. I know Deltec makes one, I'm pretty sure Bubble King does as well, but prepare to shell out big bucks and I'm not even sure they are short enough.
Have you considered running an external skimmer like a recirculator that can be set outside the stand? Perhaps you could enclose it in some sort of cabinet. Alternatively, you may look into running two smaller capacity skimmers instead of one big one. I have an Octopus that I'm pretty sure is no more than about 18" tall, two of them would be great.