Ofrei sells 1861s, but like everything on Ofrei it's pretty expensive
http://www.ofrei.com/page624.html
You can wait and stake out eBay, and get lucky for a bit cheaper. A couple of 1861s sold recently for around $1000-$1200, new, or so the seller says.
Your best bet is to watch ebay for Omega watches with caliber 861 like the Omega Mark II. They go around $900+ on ebay but will need servicing.
Click to expand...