I HAVE FOUND IT.
Earlier, I decided to melt a piece of Mozzarella-flavored Vegan Rella cheese on a saltine cracker as a snack. Upon biting into it, I noticed that it almost tasted like alfredo sauce-- it's kind of watery (not gooey like the real stuff), but very creamy tasting.
Later on, I conducted a little experiment.
I made some quinoa noodles and drained the water off of them. Stuck them back in the pot with a few cut cubes of the Vegan Rella.
The cheese solidifies after being melted if it's out for a few minutes, so I added about 1/4 cup of water to dilute it, as well as about a tablespoon of vegan parmesan, and some salt, pepper, and oregano to taste. A few more teaspoons of water and some stirring on low heat later, and I had some outrageously good vegan Alfredo sauce.
I really did try to get a good picture, but I've got very poor lighting around here, so this will have to do:
Note: The noodles were yellow, not the sauce.
Anyway, in comparison to the vile stuff I've made with silken tofu and nutritional yeast [among other things], this is, by far, the most like real alfredo. If I had some vegan margarine, I'd probably have added that too, but it's quite nice without it.