I don't have a G2 40 (and I assume you mean the "big" version and not the "C" version). If I did, I'd measure it for you. However, this raises a question. How does one measure a slide (and what measurements do you want)? I assume all three (H/W/L) dimensions vary based on where the measuring is being done. I'm not really a gun guy, so I don't know if there is some "standard" means of measurement, but if not, you may want to explicitly state what/where you want measured so you don't get apples when wanting oranges.
I do have a G2C 45 and had no trouble finding a Tagua holster just last year to fit it perfectly. I believe they also have longer holsters for the G2 model.