CMSNL have the kits listed in two ways as the kit 16010-MN4-003, which I think is a complete gasket and seal kit, (OEM), and superceeded by 16010-MN4-305, which I suspect is the gasket and seal kit for ONE carb only. they have them in sitock but,if anyone uses them, make sure you check with them by e-mail first - they can be a little slow stocktaking.If you need a cheap used set, (the rubber gaskets can last ages if looked after), try cheap carbs on e-bay from similar bikes - CBR400s esp.Hope this helps
http://www.cmsnl.com/honda-cb400f-cb-1-us_model1010/partslist/E++1601.html