Thanks for posting the link to BelMetric, @dguy . I think I've found an equivalent part for the FD01-28-114 bolt which is no longer available from Mazda. The one I found is the same thread pitch, length, and JIS flanged so it uses a 14mm socket. https://belmetric.com/jis-flange-bol...0X1.25X100PCLZ

The only difference I've noticed is the unthreaded length is a little shorter than the original Mazda part, and I'm not sure if this is important or not. Here's a video describing what I'm seeing, I'm hoping some suspension or fastener experts can chime in with an opinion.

I can clean up the original bolts or find used ones, but the original locknuts tend to warp the threads when they are removed. I think I've found replacements for the locknuts as well, and if everything works it would be inexpensive to just replace all the nuts and bolts if the new ones get warped when removing the locknuts. Hopefully that won't be an issue soon, as it seems the bushings and pillowballs last 10+ years.

 

so if you start with the Mazda part number, the ones starting with a 9 are going to be JIS standard parts, and the size is in the part number
if its a normal part number, there will be some difference

for example, 9078-60-616B or more clearly 90786-0616B
9 = hardware, it'll be JIS standard, they do bolts, nuts, screws, washers etc
0786 = style of the part, this one happens to be a bolt with a captive washer, and no ransom note.
06 = diameter, M6
16 = length of the bolt, this one is 16mm
B = if there is a letter, it denotes the plating. blank is a gold zinc, B is Black (or dark)

since its a JIS standard part, we know an M6 is a 1.0 thread pitch with a 10mm head.

9994-00-801 is an M8 Nut, M8 is 1.25 thread, 12mm head, gold zinc...

the hard one is the M10, i think typically its a 1.25 thread, but Mazda uses 1.5 for the exhaust stuff

and again, if its an FD01-28-114 is a normal part number, so its somehow not a JIS standard

 

Good video!
I would feel totally comfortable using the new bolt you sourced. I would also feel comfortable reusing the old bolt.
@JP3 Motorsports offers plating services to restore those old bolts FYI.

 

Rad. I'm always glad when people find what they need with companies I've been happy with/have suggested.