Outlet Expansion Fittings

[tcampbe1]

I want a gradual expansion fitting for the outlet of a PRV to reduce back pressure, 2" to 3" NPT. Swage nipples appear to have a large (>10°) included expansion angle. Another idea is an eccentric PVC reducing coupling. (I can use PVC for this.) Does anyone know:
1) Included angles on swage nipples, and what suppliers have the lowest?
2) Other ideas for a gradual expansion?
Thanks,
Tom Campbell