Cutout/reducer that bolts directly to header flange?

Most all of the kits are designed to go 'inline'. That's why you don't see what you want. However, you can easily have a local place weld on a 3 bolt flange to one end. Another option would be to combine these two kits if you want to avoid any welding.

Dual Electric Cutout Kit w/ 2.5" Y-Pipes HVE10K (pypesexhaust.com)
3" Header to 2.5" Pipe Collector Reducers PVR16S (pypesexhaust.com)

If you decide to go the welding route, you'd get these flanges instead of the collector reducers. You'd also have to slightly expand the Y to fit into the 3" flange hole.
3" Collector Flange 304 Stainless HVF13S (pypesexhaust.com)

If you want a member price on any of these, shoot me a PM.

Chris