There is a specific stand for these models from Casio, but those are for when you plan on keeping it at home and want a more decorative stand.
If you're planning on gigging with it and want something more portable, you can use just about any stand. These things are so light that most stands are overkill, but they will do. I have the PX-3 and I use a platform stand similar to this one.
The only thing to watch out for these is to make sure the leg sets are fully extended and locked. I'm talking about the hinges and locks like on the folding tables you use at a community center or something, not the leg extensions to adjust the height.
Another tip I have is to use Velcro to attach it to the stand. Again, these Casios are so light they can slide around a lot otherwise. Unless you find that the feet of the keyboard fit into notches in the stand, but it still might move around some. The Velcro makes it much sturdier.
Thank you for your speedy reply! I appreciate your suggestions, and I'm going to order the Platform Stand. When my son had this keyboard he used one of those X-type stands. It wasn't very sturdy and was wobbly. Now that it is mine, I wanted something more substantial, but not necessarily decorative. I checked all the sites I could find for a stand specific to this model, but guess it is now too old. Also, thank you for the suggestion about velcro--makes sense, and I will do that!