I actually posted[1] about this a few days back I think.

So the format of P2PKH sigscript is the signature followed by the public key. So basically, extract the sigscript, identify the signature and there should be a OP_Pushbytes_65 (since we're talking about uncompressed) which is 41 in hex. You should get the public key pertaining to that specific address.

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You can probably write a script to separate and identify the public key pretty easily.

[1] https://bitcointalk.org/index.php?topic=5302887.msg55912788#msg55912788