The quickest way to gain shadowy, by actions, is to use “Invite a friend to a spot of suspicious loitering” to get hastily scrawled warning notes, and then turn those in via “tricks traps and treats”. That gives an average of 7.2 CP per action, with no menace increase (though it does a lot of damage to your Making Waves and your Connected: Society, if you care about those). It also requires a friend (or an alt). See http://fallenlondon.wikia.com/wiki/Invite_a_friend_to_join_you_in_something_rather_shadowy. for exact results.
That does of course only work while in a brief section of the Bag a Legend! ambition.
Receiving Gifts of Adoration from friends/alts and using the second chances for stats may be the best. Consistent 2 second chances per action, ~25 shadowy every 5 second chances. A little over 7 shadowy CP per action. Of course, you’d need an army of helpers to actually get that many gifts of adoration.
If you want to do it 100% by yourself, that might be very viable as a Shepard (from the soul trade fate story), since you can eradicate your menaces easily. Normal wounds and scandal reductions aren’t so easy, even with social actions.
I might suggest heists for someone end-game wanting to restore their shadowy from trips to the nadir (free 20 after every heist).
edited by Kaijyuu on 4/25/2017