[Elecraft] 10 MHz external reference

[Gary Smith]

I ordered the K3EXREF and thought it was the oscillator itself which 
would provide the external signal source to the K3s. I thought this 
was all I was going to need but I see now that is not the case. 
Looking on the Elecraft order page, they don't sell a reference 
source.

What external 10-MHz reference signal source might I find get that is 
not terribly expensive that will do the proper job and allow me to 
get this working?

Thanks & 73,

Gary
KA1J