Where can I get a circuit for a
balance modulator?

P.D.-

Many, if not most SSB rigs generate DSB-SC and flter-out the unwanted sideband.
Therefore, it may be easier to generate DSB by modifying an existing SSB rig,
replacing the SSB filter with a wideband AM filter.

I haven't listened lately, but years ago there was a foreign broadcast station
just above the Fifteen Meter band, that was broadcasting DSB-SC. The carrier
wasn't completely suppressed, so I suppose this is "VC" or Vestigal Carrier! I
think the station was out of Quito, Ecuador.

This station was intended to be received using a synchronous detector. I had
no trouble receiving it on my SSB rig. I could even get music to sound OK by
careful adjustment to match their frequency.

73, Fred, K4DII