Don't turn K-band off, I had a squad car light me up with K-band on Guildford Rd not long ago. And it's fkn awesome for highway and country driving. You should, after a while, get to know what is a false alert and what's not.
K - in-car radar and automatic doors, doesn't bother me when it falses.. just keeps me on my toes. (Possibly also some industrial alarm systems transmit on this frequency too)
Ka - multinovas
Laser - self explanatory
X - not used here.
Yes, you can turn each band off.
As for where to buy them, I got my Pro-78 from radars.com.au, they're in Morley and the dude is a great bloke to deal with.