Here is a link to a page that came up on the 990 list.  His buffer looks 
good and is $37.  I think he has other stuff as well.
Link is

http://k4avu.webs.com/apps/webstore/products/show/1298607

The odd thing about the ameritron is it doesn't do quite like the adds 
say.  It does work, but with kenwood radios, only way to key  it is using 
the internal relay, not a bad thing, but you can't use logic levels as the 
add implies.  Just be ware, high and low logic levels don't work on the 
704, must use relay contacts and if you make your own cable, the common on 
the relay isn't common to ground.  They work fine and I use a couple, 
actually 3 of them on various radios, just f y i stuff.
73
Butch
WA0VJR
Node 3148
Wallace, ks.