Where can I get one of those?

In APD #325, I quote, 

<The real danger comes from dealing with AC currents as opposed to DC
currents, and this is why no one should ever put a 120v AC line source into
their aquarium.  You see, AC currents have the ability to defibrillate
your heart muscles, and cause cardiac arrest.  It doesn't take much to do
it, either - as little as 10 milliamps AC current passing through your
heart spells big trouble.

Why this tirade?  I just wanted everyone to be clear on the fact that the
real benefit of using a transformer for undergravel heating cables is NOT
that you reduce the voltage from 120 volts to 10 volts (or whatever).  THE
REAL reason is that you convert a potentially fatal AC line voltage to a
much less harmful DC voltage.>

Where can I get a TRANSFORMER that changes 110 Volt AC to 10 Volts DC?

:-) :-)

(hopefully my last comment on Voltage, etc.! :-)   Titanium Grounding probes
WILL trip your GFI.  Yes, you CAN be electrocuted by 10 Volts DC, but you
have to really concentrate on getting a palm-to-palm or from one side of the
chest to the other current, bloodstream to bloodstream. Dry skin has too much
resistance.  In other words, you have to have your hands (or chest) wet with
salt water or urine in order to get a fatal current.  It usually takes a
pretty significantly long shock as well.  Children have been electrocuted by
a 12 volt car battery, which the father had hooked up to the bed to "change
the behavior" of a child who wet the bed.  Yes, AC is much more harmful.
 Defibrillators use a very powerful DC shock to stop the fibrillation, so the
heart may resume normal beating.  DC does stop the heart.  But it often
restarts.  AC really screws up things, by causing fibrillation.  Almost
always fatal, unless medical help with a defibrillator (or CRP) is
immediately used.

Please be careful.