On the right is an LP hose from a 2005-current Performer, as removed from the regulator, although I think it's the same thing on the other end where the orifice attaches. It's NPT thread (tapered) but I don't know the size. Do you?
On the left is "regular" thread also of unknown (and slightly different) size, since it's not tapered.
I wanna connect those two with some sorta adapter, yeah?
My local propane dealer was completely mystified by all of this.
At the bottom of the image is a normal 3/8" connection.
No photo, but.
Most full service auto parts stores stock
a huge assortment of brass fittings.
Try to find a bigger NAPA or independent.
Places like Advance, Auto Zone, etc are a waste of time.
The Ace near us has a pretty selection also.
Sorry, forgot the picture. I'll try Ace, but my only other options here are the non-Napa auto parts chains or TSC.
This sort of thing, if available, is likely found easily online, if I knew what the sizes where. (Chicken or egg problem at the moment.)
Yeah, I forgot about TSC.
Lots of brass there.
Good hunting.
@Hank Hill got your ears on?
The top threads appear to NPT as you suspect, if it is indeed NPT then once you figure the size (which may be 3/8 or possibly 1/4) the thread pitch is set by the fact it is pipe thread.
The bottom fitting is a flare fitting, typically called a hose fitting use mostly on hydraulic hoses. The flare surface provides a good sealing surface without the need for o-rings. The flare can be different angles, 37 degree is the most common I believe as it is an SAE standard flare.
This is just my thoughts based on the photos. I know my Lowe's and Home Depot has a good selection of brass fittings in the plumbing section.
I hope you can track down the parts you need.