Thanks for your comments and suggestions. The smallest appropriately composed silver rod I've seen so far is 1/64". It probably is available in smaller diameters.

Wouldn't heating the lugs to about 500f and perhaps chilling the tubes cause at least 2/64s of an inch of expansion/contraction temporarily? I use this method for installing steel crown races, and the inner diameter increases visably. After cooling they are tightly mated to the fork. Condensation might be a problem if the tubing was cooled.

The kiln would apply heat very evenly, which hopefully would cause the filler to spread in all directions.

It may also be possible to make clay funnels to guide the silver into the lugs rather then attempting to put it in place before hand.

I will probably get a fork crown and blades to experiment with. Or building a stem from the lugs at bikelugs.com would be nice and I would have a better chance of survival in case of catastrophic failure... but they are rather expensive.

Perhaps I should just learn traditional brazing?

Thanks again.