Finally found one source for vacuum grease.
VWR Scientific has an on-line catalog available.
Probably available in other scientific/lab supply catalog/suppliers.
The VWR net site for this product is below:

http://www.vwrsp.com/catalog/object.cgi?cn=59344-055

You can order through the 'net from them.

It's $13.18 for a 5.3 ounce tube.  That's enough to easily do over a 
dozen busses, and leave enough left over for dessert.  It's about the 
size of a large tube of silicone sealant.

In other words, share this stuff generously with others and your 
grandchildren will STILL be using the same tube.

 - - - - Warning - - - -
This is a silicone grease, I have only used it in limited locations 
in my bus.  I suspect that gasoline will dissolve this stuff, haven't 
tried.  It is VERY slippery stuff when freshly applied.  Put it on a 
metal tube put your rubber hose on that, crank down on the hose clamp 
and it will still slip around, as I said, very slippery stuff.  It 
eventually hardens, well actually it gets sticky.  It is designed for 
vacuum, not pressure.  Put it on a joint with pressure and the hose 
clamp will NOT hold it in place.

A little bit goes a long way.  Smear a little on the suspect joint 
and assemble. I used it on the fittings coming out of the manifold 
going to the vacuum booster and brake booster, and the metal fitting 
on the air intake.

> good tip. you got a manufacturers part # or...?
> $9 sounds cheap compared to the hassle time spent seeking/fixing leaks.
> i'm to the point of doing a one time disassembly/goop/reassembly as a
> pre-emptive strike against vacuum leaks.
> 
> thanks much,
> dwight

- Jeff