Old Kemtron C-16 kits sometimes show up, but they’re steam and HOn3, so probably not of interest. Many of the parts can be obtained through PSC, though not complete kits.
PSC also produced kits for the WP&Y Alco DL-535E diesels, also in HOn3 and no longer in production.
My write up on building it is at:
http://cs.trains.com/mrr/f/88/t/210285.aspx
The British are especially regarded for their loco kits. Pretty much non-American, it’s possible there’s something suitable for conversion.
If you want to build an electric, I’d first suggest looking for a possible donor for the drive. That would leave you the superstructure, etc, which might be plenty of challenge in itself.