The halons used in fire suppression systems are no longer manufactured due to the severe effect of halon on the ozone layer (much worse than the also banned Freon). All the halon available today is recycled from fire protection systems removed from service (and often replaced with newer, less environmentally dangerous systems,) Portable halon extinguishers are illegal in many locations. Some details are in this
EPA post
You are correct that many dry powder extinguishers sold in hardware stores can severely corrode the items that come in contact with the powder. But remember that the first purpose of fire protection is life and safety protection. Things are replaceable, people aren't And your best protection of things is to have a good insurance policy.
If you want an extinguisher that is legal (everywhere) and won't damage your electronics, get a CO2 extinguisher. However, unless you've had firefighting training, if the fire is anything beyond the smallest fire, call the fire department, and get everyone out. Let them put the fire out and stay safe.