Just off the top of my head, I believe it was repealed with the passage of the *Dick Act*, technically the The Militia Act of 1903, together with its 1908 amendment which created the structure of today's National Guard.
The act divided the militia into two groups: the Reserve Militia, defined as all able-bodied men between 18 and 45, and the Organized Militia, defined as state units receiving federal support. There was a one-time grant of $2 million to modernize equipment, and states could now use federal funds to pay for summer training camps.
I don't have the specific text of the Dick act, but it ought to be findable now that you know the legal name, approximate dates, and popular name for the legislation; if you can't find it with that, let me know and I can likely get it from my local Library of Congress Government Depository library; but I'd be very surprised it it isn't on the internet somewhere, likely at Thomas.
-atchy-/-
That being said, the 5th Circuit's Emerson case said that you don't have to be an active member of the militia in order to be protected by the 2nd Amendment. Thus, the actual definition of militia is, while historically interesting, not that important for legal purposes at present. It does, however, help to confuse/piss off lieberals to tell them that they are members of the militia.