Does anyone have quick reference to the DOL's policy for locating and handling account balances of lost participants?

I'm not sure there is a "policy". The following excerpt is from an article in the Journal of Pension Benefits; Volume 2, Issue 1, Autumn 1994; Handling "Lost" Participants By ELINOR R. MERL and FRANCES G. SIELLER:

"The fiduciary responsibility provisions of Title I of ERISA provide no specific guidance on locating lost participants. In an opinion letter, the DOL states that the determination of whether the fiduciary has taken adequate steps to locate lost participants is based on facts and circumstances. [The Washington Service Bureau, ERISA Update, File: DL 0086] However, it also suggests that, at a minimum, the employer should employ the Social Security Administration (SSA) to attempt to determine the current mailing addresses of lost participants."

If you want a copy of the article, email me at gself@houabg.com.