I'm out of the house now, so don't have access to my files. For now, try Moss Miata or MiataRoadster.
I'll confirm those guesses later.

 

The quote below (blue italics) and the diagram come from M.Net. It appears that the parts are available from Mazda. I originally thought you were talking about the rocker panels (beneath the doors). This is likely more applicable. Once installed, I would hit them with a good rust proofing paint.


the inner and outer frame rails I ordered are part numbers; NC10-54-35XA and NC10-54-310, respectively. These are for the LEFT side. The RIGHT side is one number different. My body shop claims they can cut out the rusted section and piece these back in.

 

I checked Rockauto but didn't see that piece in the body section.

If you check the rocker panels, they are known to rust sometimes.

 

The body is solid, no rust anywhere.
I discovered rust through in the frame where the front roll bar attaches.
I'm told someone makes weld in repair pieces with the threaded bolt holes in place.
These are the items I'm trying to locate.

 

Take a look at these: more to your liking ?


Miata Frame Rails

 

I found the exact items I need sold by The MX5 Restorer. Co. UK.

I'm hoping someone in the US also makes them.

 

Reinforced replacement sway bar mounts

 

If I did this correctly, this is a picture of the repaired frame. The welded pieces are available in the UK. I'm hoping to find them here in the USA.

 

drove it for the first time in over a month. Relocated from MD to NC, but I had a 3+ week gap between houses, we were forced to stay in hotels. Moved into house yesterday and finally got the Miata picked up from a friends house. Felt really good to run through the gears.

 

I know what you mean. It always does after you've been away awhile.