Well, usually when one plays a very early g3, they also fianchetto that bishop, (otherwise what's the point?) and often play the king's knight to f3, and castle. When they do all of this it usually amounts to a King's Indian Attack type of setup, and there are books on that opening.
1.g3 book?????

What system do you want to play? Alekhine Reversed (1. g3 e5 2. Nf3), Reti (kingside fianchetto, Nf3 and c4), KIA, fianchetto d4-c4 openings, fianchetto d4 opening or what?
ChessBase can be used for making your own repertoire, and/or finding a player who plays the same as you want to play.
A BOOK ON 1G3 IS : "THE WHITE SNIPER MANUAL" BY CHARLIE STOREY 2012... PRICE $ 50.00 US DOLLAR...REAL EXPENSIVE COMPARED WITH OTHER TITLES...DON'T KNOW IF THE BOOKK IS THAT GOOD....

I start my Hippo with 1.g3, but I can't think of any books dedicated to it. Nigel Davis created a Chessbase course on 1.g3 in 2010 called... 'Bamboozle your opponents with 1.g3'
This is the trailer for that course
https://www.youtube.com/watch?v=eJIO5osEiYM

Can also transpose into a Catalan
This is your contribution after more than 11 years?

I never realised that guy bumped an ancient thread.
I answered like it was posted yesterday!! 😂
How did he even find this thread?

Got bamboozled by a 1 g3 player, googled to look for some theory to avoid this scenario from happening again in the future and ended up here without looking at the date/time of earlier posts. Looking at it, I think most of the theory on 1 g3 is found (transpositionally) in the lines mentioned in earlier posts such as the Reti, KIA, Barcza system, Hippo, English, Catalan, Double Fianchetto. To add something new to this is not easy: books on Flank openings may also help out : the books of Keene or Kotronias, or Euwe's series in earlier times. Books on unusual or off-beat openings may contain small chapters on 1 g3. ECO A has only one small subchapter dedicated to the immediate 1 g3 in A00. I found the dvd: Foxy opening Unusual openings - A repertoire for black against , b4, a3, f4, g3, g4 and Nc3 - dvd by Andrew Martin. So far, I haven't be able to find an extensive repertoire book for White on 1 g3. I'll need more time to do research on this.

Got bamboozled by a 1 g3 player, googled to look for some theory to avoid this scenario from happening again in the future and ended up here without looking at the date/time of earlier posts. Looking at it, I think most of the theory on 1 g3 is found (transpositionally) in the lines mentioned in earlier posts such as the Reti, KIA, Barcza system, Hippo, English, Catalan, Double Fianchetto. To add something new to this is not easy: books on Flank openings may also help out : the books of Keene or Kotronias, or Euwe's series in earlier times. Books on unusual or off-beat openings may contain small chapters on 1 g3. ECO A has only one small subchapter dedicated to the immediate 1 g3 in A00. I found the dvd: Foxy opening Unusual openings - A repertoire for black against , b4, a3, f4, g3, g4 and Nc3 - dvd by Andrew Martin. So far, I haven't be able to find an extensive repertoire book for White on 1 g3. I'll need more time to do research on this.
Thanks for explaining! 🤣
The 'Foxy Openings' series brings back memories. Andrew Martin, Daniel King and many others did their first instructional videos in that old series.
I was wondering whether there was any book written on 1.g3 as I couldn't find any on the internet