Righty,
I always have a bit of a theme with my characters as I develop them through their survival, or terrible deaths, and I’ve figured out which one I want for this character.
I’mma make them an elf~~~~
From my experience, I’ve only found the file once in a prior run in the sewers.
Are there any other spawns to know about? My hunt in ye’ old’n Google didn’t get me the information I crave to become a champion of nature.
I’ve always found the book in places where trash is; check trashcans, check street sweepers, and check basements. I once spawned in a house with one in the trashcan.
It’s probably going to take some dedication since the standpipe maintenance log is somewhat rare to begin with and there are two identical versions of the book, only one of which contains the recipe and the only way to tell them apart is to read one. The good news is if you find the one without the recipes and do the initial reading, all the identical ones without the recipes should no longer show up in red so the next one in you find in red is basically guaranteed to have the recipes.
Aside from that, I know veterinary clinics can have books like that, so it might be among their number, but I’ve never found it specifically there, and labs probably have it.
Edit: I just remembered that you don’t necessarily need to the read the standpipe maintenance log to determine whether it has the Elf-a formulae. The description of the book will tell you that if it has them without having to read it, but you’ll probably want to anyway just because the one without them seems to be the more common of the two, so being able to tell them apart at a glance could be useful.
I agree, IIRC I found the “book” in a lab once (at least). As I remember, I found the “book” few times by long-playing characters eventually, but I don’t remember exact locations.
Just perform full-cleaning in several cities from top to bottom and several labs from top to bottom and you will find it too 
really common in labs find a lab with a tunnel system and go scraunging around
Odd, once upon a time they were only in places like the Sewer Treatment facilities and whatnot.
Now they’re once more in Labs for us avid adventurers eh?
Wondrous, time to get my steel knuckles, gas mask, and iodine tabs and jump face first into a facility swarming with brutes, shocker brutes, and a hulk or two (I’m closing in on a full year in-game, so these boys got beefy).
I’d hunt around open sewer works. the ones usually crawling with Technicians and a shocker. I’m not sure if a Tech was carrying one, or if it was laying around in the tent lockers.