We've been thinking of getting some more toys for Kel the Purple (and any other children in the system who like playing with such toys) but so far, xer absolute favorite are the interlocking discs that we got from the local dollar store, and the sad thing is that they never got any more. That's typical of the dollar store; they get neat little things and then after a while you never see them again. Kel's button collection came from the dollar store, and they don't sell the little jars of assorted buttons any more.
I was certain that the dollar-store discs were probably factory-seconds of some commercial toy, but I'm not so sure now—there are toys that are functionally identical to these discs, but they look tellingly different and I'm not sure how well they're bound to interlock with the ones we got from the dollar store.
There's "BrainFlakes", pictured here: 
Obviously it's the same sort of toy, and they're said to be 1.3 inches in diameter; I measure one of Kel's discs at 1.29". But to my eyes, anyway, the BrainFlakes have a larger central hole and the edge slots look a little deeper and wider.
There's "ToyLi" discs: 
Now these look to me like they're more likely to interlock with the discs we've already got. The slots look like they're closer to the right dimensions—but these discs have letters in the middle, instead of just a round hole!
And if you hunt around Amazon looking for "interlocking disc toy" or similar, you'll find a number of products that have a similar general appearance, but they're all a little different from one another.
I'd like to put in a request to the family to buy one of these options but I'm not sure which is most likely to work—I don't suppose it's entirely necessary for a new set of discs to match the ones we already have but it would be nice to give Kel the largest possible hoard to play with.
~Chara