Thread sizes below 1/4 confusing

Many fasteners "do not exist" because the auto manufacturer had them specially made, and nobody else ever put them in stock, or had any use for them. So when they were all used up, there were no more made. A 10-24 nut with a 5/8 captive washer "does not exist". You can look thru every catalog like McMaster, Fastenall, or Graingers, and you won't find those. Add to that the integral rubber seal, and finding them just became 100X more difficult. What you will be able to find is regular 10-24 nuts, 5/8 (or so) washers with a 3/16 hole in metal and/or plastic, so that's what you'll need to use. You could superglue the 3 components together or something (I'm assuming the reason for it all being integral is for ease of assembly). McMaster p/n: Nuts 91841A011 $3.77/100 , .450 dia #10 Nylon self-retaining washers 91755A220 $4.61/100 , 1/2" dia. #10 washers 92141A013 $3.30/100 , 1/2" x #10 rubber washers 90133A017 $10.33/100 .