Hi

Mathewt
yes, you can use ferrites of power supplies of VCR, tv sets, I am using ferrites of old monitors, old power supplies of telephone systems , japanese and german, and also of old power supplies of PC, faxes, of different sizes, BUT my CDI have only two windings, because I am using as switching supply , step up transformer I believe you say, from 6 volts I can reach 400 volts and the best pieces a bit more than 500 volts.
Caution, the sides of ferrites must be clean and the contact surface between halves must be clean, if you have small foreign particles you never reach good output voltage.
I believe you can use it because the power they can manage are big compared with the power comsumption on a spark, you never reach saturation, you are working in the linear stage.
If you like see Amidon ferrites, search in the web, they are fine person and sell ferrites for CDI
also wire.
I have the better coils , more than 500 volts of pot cores OL N30 from EPCOS, a siemens subsidiary
www.epcos.com
my system is like the you see at
www.qsl.net/ariparma/trasfo.htm
but mine start from 6 volts and have a CD4047 cmos oscillator, far better stability than the 555 and the switching transistor is a TIP 31 VERY GOOD BRAND only , throw away cheap chinese, the bridge rectfier you must made of fast recovery diodes.

c moore
You can use any high voltage coil of a moped with CDI, I am using with success coil from Honda Transalp 1993, same as Honda XR 600.
Very sturdy but bigger than of 3W, and this coils are designed to make a spark with low input voltage , my memory fail but I believe I measured a bit more than 100 volts at the capacitor when kicking to start the moped ( DAELIM , honda based moped magneto on Honda transalp coils).
I make it spark with 200 volts output of CDI when I am in the first stage, but after improved and reach 400 volts .
The best I have, more than 500 volts are from a german switched power supply, recycled of old telephone equipment and wounded with wire recicled of old relays of more old telephone equipment , also german, with a hand powered drill, What a technology!

Good luck and better sparks.
sorry my english .
See you later
Jose