Where to find bolts for an old Raleigh Bicycle?
I spent my formative years in a Raleigh Five Star Dealership that just so happened to buy up all of the vintage Raleigh mudguards of the steel type for 26" wheel 3 speed bikes. (Raleigh had a warehouse clearance.) That was in the UK and we had mudguards for everything going back to AFTER the requirement for the white panel on the rear mudguard. Nothing from the the 70's onward had the bolt type you describe, although we also had a lot of frames including ones with the 7/32" x 26 TPI eyelets. Sounds to me that you either have a U.S. special, something really obscure, something really, really old or something after-market.

I suggest that you put some new mudguards on there. It will be a lot less hassle.
For those new mudguards you can drill out the existing holes or use 5mm nuts and bolts, obviously with a fair few washers in there.

If you want to keep the retro look of the existing mudguards, you could make your own 'P' clips with a bit of tin, some snips and a drill. These could then be attached with a metric nut and bolt.