We used to be able to get 94 octane at Sunoco stations, but I have not seen it for a couple years.
My local airport will dispense 100 octane Avgas into 5 gallon metal cans. Cost is $4.75/gallon.
I don't do it often, but I will occasionally mix the 100 octane Avgas with 93 octane pump premium in my 3.2 Carrera Sport and it runs like a scalded cat!
Have not tried the mix in my Boxster yet, but I will soon.