Political Money Online has issued a report (available to paid subscribers only here (I think, as I’m not a subscriber)). On the free portion of the website, it explains in pertitent part:

….PoliticalMoneyLine has gathered information on the national lobbying efforts to change the federal campaign finance laws. During the last ten years the Campaign Finance Reform Lobby spent close to $140 million – very little of which was reported under the Federal lobby Regulation Act. Practically all of this was done through non-profit 501c organizations.
The campaign finance reform effort involved donations of almost $140 million to nearly one hundred organizations that educated people to the problem, mobilized support, and sought legislative and legal remedies. This also involved paying lawyers, academics, business leaders, media groups, and even getting involved with federal election campaigns.
This ten-year lobby effort is small in comparison to the other major lobbying campaigns. And it is only being disclosed now because of disclosures by the major foundations involved and some of the campaign finance reform organizations. In general, most 501c organizations do not voluntarily make their donors public.

BNA reports (paid subscription required) on the reactions of some of the groups to the report. Readers interested in this subject might check out this old article from the Philanthropy Roundtable. I also recall that there was a report a few years back from a conservative think tank called something like “Who Funds Campaign Finance Reform?” but I have not found it through a Google search.