Kick 3.5 ROM?
There is no such i'm afraid. If you mean the ROM Update to use OS3.5 - OS3.9, that is just a file. Not a real EPROM. Dunno if it could be put into a ROM manually and just skip the ROM Update when booting Amiga. I know there is a hack by Harry "Piru" Sintonen that patches some functions and the exec.library in 3.1 ROM, but that's still not a 3.5 ROM nor an official replacement.
You can find that patch on his homepage. It will update the ROM file and save it. So you can take that file and burn an EPROM and use that instead of the original 3.1 ROM...
Sorry, can't help much :/
