Spousal visas (CR1/IR1) are generally processed at the consulate in the country the beneficiary spouse is living legally. If it is a country where the U.S. does not have a consulate, then there will be other options. Many folks file the I129F after filing the I130 in hopes of speeding up the process, but you are correct, K3s are rarely processed. Regardless, in either case, the step are the same, the U.S. citizen files a petition, USCIS processes it. When the petition is approved, it moves to the NVC which will require the USC petitioner to upload supporting documents. Then NVC routes the petition to the proper consulate and the beneficiary schedules a medical exam, and a visa interview.
This may help.
Good Luck!