This has been an interesting topic to research ... and really makes me wish I had paid more attention to the documentary they did on the history of "Colonel" Harland Sanders and the founding of KFC - they showed film of him and his original pressure fryers.
The "original" Original KFC was cooked in a cast iron skillet ... because it was less greasy than deep frying .... but to decrease cooking time and increase output (and thus profit), he started playing around with pressure fryers which could cook more chicken in a shorter time. The original ones the he used were on-the-stovetop types. And, apparently the method he used of marinating and then breading and frying is known as "Broasting
" ... you really want to take the time to read this article
The two main commercial pressure fryers appear to be the Broaster
and the Henny Penny
... and both will set you back a pretty penny when new ... and even used they are upwards of $2,500 US (for a Broaster currently on eBay - Broaster only sell new to restaurants so I couldn't find a price for them ... although I did find a price for a Henny Penny, starting at about $9,000 US) ... and you have to have commercial wiring to handle them - your average home wiring will not handle it. Obviously, these are both overkill for the home cook.
This site is also a must read: What You Need to Know about Pressure Frying (and don't forget to read the other associated topics on that page, too!!) The only two pressure fryers she mentions are both hard to find.
One option that might be worth exploring is an All American Pressure Cooker
- you'll just have to email them and talk to them about if it can be used as a pressure fryer. It certainly "seems" to fit the bill ... no rubber gasket, dual vent ports, multiple locking clamps. They don't advertise their cookers as "fryers" - you'll just have to ask them about it.
So, basically, the modern day "drive thru" KFC secret is based on marinating overnight (to help retain moisture like a brine will), then the breading with "11 secret herbs and spices" (for flavor), and cooking in a pressure fryer (to retain moisture and decrease greasyness).
Whew ... now this has been fun!