Spooner seems to have one of the most interesting takes on it all, Though I am not super familiar with him and his works.
Thoreau was also an abolitionist, and is often linked to anarchism post-facto (not without reason, but still, he never used that label, to my knowledge). Like Spooner, he advocated in support of John Brown, which was not a particularly popular thing to do at the time*
The Civil War also played a dramatic role in the life of both Albert and Lucy Parsons. Albert fought for the Confederacy in Texas, but later fought for the rights of former slaves, and actually married Lucy who most likely had been born a slave. While not a specifically anarchist act, an interracial marriage was in itself transgressive. Albert's politics tended towards the socialist, though in the 1800's the lines were much more blurred between socialists and anarchists, and, from what I know, by the time of the Haymarket Affair and his subsequent hanging, he was an avowed anarchist.
Lucy went on to help found the IWW, and in at least one instance called for the homeless and unemployed to arm themselves with knives and guns, and to shoot or stab the rich as they left their homes. I hear she later fell in with the communists, which is too bad, but to my understanding, she was one of the most incendiary and uncompromising speakers of her time (owing, to no small extent, to her lived experience...)
The Civil War is actually one of the parts of US History I probably know the least about, despite it being one of the most interesting parts. I'd love to hear answers, or get clarifications and corrections from others who know more.
*If you haven't, check out the first issue of Modern Slavery for some fascinating reading on all this.