If you're looking for a folder that can be drawn quickly, consider Spyderco's very popular line of Delica knives, equipped with an "Emerson Wave".
I've been a knife instructor for many years and had used the traditional version of the Delica for a long time, about three years ago they came out with a waved version, it is closed like a regular pocket knife, but can be drawn and deployed as quickly as a switchblade.
There are a couple of companies that utilise this design now, and brand choice is limited.
Wave blades unlike switchblades or centrifugal force knives (flick or butterfly), are not considered prohibited weapons under the Canadian Criminal Code, so it's OK to have them on your person, as long as you don't tell the police you have it for your protection or safety... knives are just tools unless you are interested in obtaining a criminal record.
Here is a demo on the drawing possibilities:
If you don't have a distributor in your area they can be purchased directly from the manufacturer or by sellers on eBay... many of which prefer only PayPal transactions!
This blade configuration also has another valuable use:
