These are not really common fittings, and my experience with reducing els is that they are pretty pricey. Much more common to use a standard el, then increase the pipe size with a concentric or eccentric reducer, unless you're really pressed for space.

In any event, you need the type of material, pipe schedule, and the flow. The Crane Technical Paper No. 410 will likely have the info you require.

Are these drip pan els installed on safety valve discharges? If they are, it's not likely an issue anyway. If you're concerned, the manufacturer should be able to supply any info required.

TBP
Your exactly right about the rarity and expense of these fittings.  This particular case is for the inlet piping to a safety valve protecting a Yankee Dryer (constructed of cast iron).  The client's design practice that must be followed originated from the ASME Section VIII Appendix M-7.  Normally, this is a non-mandatory Appendix, but in this case, with this client, the 3% non-recoverable inlet losses are a critical design attribute.  The reducing ell was chosen because a standard ell & reducer exceeded the 3% rule.  My task is to now substaniate the design calculations of work that is already completed.  The cart got ahead of the horse.
Crane TP-410 is always my first reference.  Its not covered.

Wow. A flow problem that's not covered in 410. I've never actually come across anything quite like your situation. If I find anything, I'll let you know.

I guess the upside is that if it's not in 410, and nobody here can help, then whatever answer you get will very likely go unchallenged :)