I've never seen cubed in my internet travels to billiard supply shops.
You might try the talc bags. Several different makers. It can be messy too, just not as bad.
If you take the bag out of the plastic and gently squeeze it or dab it on your bridge hand, its not as bad. However, it still tends to get all over the rails and cloth no matter how hard you try not to.
I agree -- no matter how careful you are with the talc bags, they are "poofy" and it gets all over the place.
"Solidified" cubes of hand talc do exist, although they seem to be only available outside of the U.S. -- most notably Japan and the Latin American countries. Bobby Chamberlain introduced me to the cube version of talc several years ago (that he gets from Japan), and it is exponentially more neat than either powdered talc or talc bags. Each cube is slightly larger than an ice cube; you can precisely apply it only to the areas of the skin that your cue shaft rides on, and it doesn't easily transfer or smear. A cube also lasts an extraordinarily long time -- in fact, the cube I got from him, I recently used completely up.
A couple years ago, I found a box of these on an eBay auction, from a seller in Latin America, under the term "Suavinas":
These are actually flesh-colored, unlike the ones Bobby introduced me to (those are pure white). But they are silky smooth talc nonetheless.
Short of doing international commerce to get a hold of these cubes, you can just get an ordinary "cone"-shaped talc (like that is sold for pool rooms -- it has a hole up the middle to place on a wall-mounted peg):
You'd then hacksaw or band-saw it, longitudinally (i.e. going longways "with" the hole), into four, or six, or eight "strips." Then, cut those strips into manageable pieces. You'll then have arc-shaped pieces that make it pretty convenient to precision-apply.
Just some ideas,
-Sean