Who makes the 1/4 inch driver tip(spanner) that fits the rear sight blade nut? I have seen photos but can not locate one. I could make one, but would like to add a manufactured tip to my tip block. Thanks.

The rear sight nut does not take a spanner! The nut is "staked" in place! When you need to replace the rear sight blade the screw is turned until it breaks the screw just in front of the nut. The new blade and a NEW screw with nut is installed AND STAKED in place!
jcelect SWCA#723

This page from the FAQs has the info your looking for but as said peviously the tool won't realy be required as It's not used to tighten the nut but simply spin it on which can be done with just about any tiny flat screw driver.. I made myself up a bit with the Dremel..
The FAQs
Enjoy!!
Gary/Hk

Brownell's

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Regards,
Lee Jarrett