I have found a few PARK S.A.E over time at bicycle swap meets ,fee bay ...few and far between .I have a full set of PARK metrics that I use ,work fine .Look around at estate sales ,garage sale for vintage tappet ranches ,some are thinner that others ...I have contacted PARK tools to ask if they can start making S.A.E styles again as more vintage collectors use S.A.E. on their vintage projects ..
There are a lot of very close sizes. From my days working in areas with multiple other people, the metric didn't grow legs like SAE, so I learned to adapt metric.
Many popular sizes are so close as to be nearly indistinguishable (probably closer matches with less expensive tools). Others work pretty well, but not quite indistinguishable (more like the difference between the fit of a cheaper tool vs. an expensive one in the same size). I've found the following usually work (as I said, you've a better chance of success with cheaper, less exacting tools, but I've never had issues with stripped fasteners using the following, though I'd probably get the exact deal if you're talking about a lot of torque, which the smaller fasteners couldn't handle, anyway):
5/16" = 8mm
7/16" = 11mm
1/2" = 12 or 13mm (I think I've used both depending on the tool/brand, but the conversion says it should be more like 13mm)
9/16" = 14mm
5/8" = 16mm
3/4" = 19mm
13/16" = 21mm
1" = 25mm