Impedance matching transformers

[Larry Hendry]

I am in search of decent quality audio impedance transformers for a
project.  The type I am looking for are the ones found in the XLR to 1/4"
phone microphone adapters.  I think the impedances are about 600 ohm on one
side and 10K ohm on the other.  I am also looking for one-to-ome audio
transformers in the 10K ohm range.  The ones I have been able to find so
far do not have the frequency bandwidth to be considered decent quality. 
The ones in the microphone adapters are fine.  The mic adapters can be
found made by shure, and others. Even Radio Shack sells a decent one for
$14 or so.  However, it appears to me that the transformer is the least
cost of the entire assembly.  I want to buy several to be incorporated in a
project. Paying $14 each and stripping them out of the adapters is not what
I had in mind.  The people who make these mic impedance matching adapters
have to buy them somewhere.
Anyone know where I can find these to purchase?
Thanks
Larry Hendry