Ray,
I am pretty sure you are correct that the grommets in the command control sticks would work. But, I think that idea has started to catch on, as I have been seeing these sticks go for around $10 each on Ebay recently (unless there are lots of retro computer gamers in need of new sticks). If I can get N.O.S. grommets for a little more it's worth it to me. I am still hoping to get my hands on a command control stick so I can see for sure if the grommets are the same (you can never have too many spare parts

). It is a great suggestion, and if I do get a stick for a low price I will be sure to mention what I find here.
As far as boring out a Pacman grommet, I think the real problem is that the grommets (both Pacman and the Williams style) have a metal bushing in the center that sort of forms a convex shape where the joystick enters. Trying to get the grommet drilled out to the exact size to put a different bushing in while creating the correct shape might be difficult, but it is an interesting idea.
Thanks again for everyone's help!
Dave