eeyeore9, 6 inch alphabet is really large. That might be used for a banner or something very large that needs to be seen from really far.
I do not know of any but you might be able to use a lettering like from Embird but it would cost about 150 dollars to get started, 120 dollars for the beginning software and another 25 or so for some basic lettering so you do not have to digitize it youre self.
When I first started I got all the largest letters but have not used them because I use small ones instead. Largest ones are 3 inches.