Kickstart 3.9 doesn't officially exists but the newer modules from OS3.9's BB2 "AmigaOS ROM Update" that resides in Devs folder can be used to replace the older Kickstart 3.1 modules to form it.
These modules are the following:

Using these instead of the 3.1 ones (as I wrote to my guide) will grant you a Kickstart 3.9 ROM that you can use it via kicking it (like for example with ACA accelerator's ACATune utility) or burn it into real 1MB EPROMS and mount it on your Amiga replacing the former Kickstart 3.1.
It works just fine and I've been using many of those for years
