I will need to make .69-caliber spherical balls, from pure lead to, perhaps, 1:20. Since casting balls without tangential sprue or Lyman-type teat sprue is, I believe, not doable, I suspect swaging is the method needed. Since I will not require these balls by the thousand, or even be the hundred, I seek to keep the cost of equipment as modest as I can. While I am prepared to roll balls between plate glass to regularize surface, rolling balls is not a substitute for creating regular ones from the get-go. Please identify the least expensive way to create these balls - that is, balls with as few inherent imperfections as is feasible.

I don't think rolling the ball between two flat glass plates will give you a round ball. It will most likely roll narrow flat tracks all over the surface. The way they make ball bearings is to roll the bearing slug between a hard and soft roller with channels in each the diameter of the ball.

Here is a link to a simple design which you might be able to adapt to rolling lead balls:

http://www.sheldonbrown.com/rinard/ball.htm

I'm thinking if you could get a .69 diameter U-channel machined in an aluminum block, you could have another block made from MDF board with the same .69 cal groove. Cast your lead balls and place in the groove of one block. Then place the other block over it and roll back and forth until the ball is smooth.

Another way may be to cast the balls with a tangential sprue mold, then use the mold blocks to swage the ball with 4 x 90 degree rotations.

Maybe some sort of home-made Shot Tower?

How many balls are you wanting, and what are you wishing to accomplish by not having a sprue?

Since you are wanting to use lead, you won't be able to get a durable and uniform (being a relative term) finish anyway.

I'd suggest casting them and then tumbling them with some corncob and that should disappear the sprues pretty good.

Another option for a small quantity is just polish them down by hand with some abrasive paper.

Lee round ball molds don't have a sprue tit. They cut off right on the ball surface. And you can get one in .69 from Track of the Wolf for $19.25. Or other places too.
That should solve all your problems; effective and cheap. If you have or get a Lyman mold, just file the tits off.