It will be difficult to locate an attorney willing to tangle with the IRS for free. You could try the legal aide office in the county where he resides, but there are no guarantees there.
While I echo the earlier response, the basic problem is that this could easily result in a federal criminal case and a significant period of incarceration in addition to the various penalties and interest that could be assessed in this situation. The U.S. Department of Justice provides a lot of information about tax crimes and other federal offenses in what is known as the U.S. Attorney's Manual, a multi-volume set of resources which is publicly available and indexed on the website. Most of the relevant parts appear in Title 9 of this publication. I have provided a link to the Criminal Tax Manual pdf file. The bottom line is that this situation is very dangerous. As to the expense involved, an analogy is in order. A person who suffers from a ruptured appendix could, perhaps, remove it himself or herself and avoid the expense of a trained surgeon and may even survive. Few, however, would consider doing it or advise it for obvious reasons. The same holds true in this situation.
I too will echo the earlier answers. It is important that the this problem is solved correctly or the consequences (criminal prosecution) could be severe. I'll add that a possible option for your brother would be to seek the advice of an attorney who is familiar with the IRS' informal "voluntary disclosure" policy. While there are certain requirements (i.e. no IRS action encouraged your brother to come forward), if your brother qualifies, he may be able to limit his filing requirements to the last 6 years and only have to pay tax, penalty and interest related to the 6 years filed instead of the full 20 years for which failed to file.
Frankly, if he has been receiving 1099's it is probably only a matter of time before the IRS catches up with him.
For your information, I'm attaching a link to the IRS website discussion of the voluntary disclosure policy.
You may find some legal assistance through a taxpayer clinic. I would firs look to see if a law school or business school has a clinical program. These programs are often at little or no charge. You should also contact the county and state bar associations for referrals and information. Often there is a list of lawyers that handle matters on a "pro-bono" or free basis.
As noted by the others, there are serious and expensive consequences if not done properly. The voluntary disclosure program is worthwhile. It is extremely important that all returns filed be accurate and complete.
The worst course of action now is to continue to ignore the problem. It will not go away and the best opportunity is to come forward voluntarily, not when the government begins its investigation.