Home Depot in their DeWalt bits,used to have a selection of 2-3 in a holder,so try there.
you may want to cross-reference nautical supply houses/outfitting places. Lots of cross-head screws are used building boats (like frearson/R+P etc). If you need bunches of them, Apex probably is good for an industrial brand. Small lots, snap on is not bad because they sell everything in singles. The big bx stores may be hit or miss depending on local conditions/market needs, but maybe try there first if you need something immediately.
Didn't realize brakes used Frearson/Reed&Prince screws. Seems a bit odd, but I never understood why they exist other than as a historical oddity and/or traditional niche applications (I.e. nautical).
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