So far as I know, there are 2 free mock exam sites:
http://www.jdiscuss.com/Enthuse/jsp/ShowAvailableTests.jsp and
http://j2eecertificate.com/ JDiscuss.com provides mock exams for both 1.3 and 1.4, while
J2EE Certificate.com provides mock exams only for 1.3.
Hope this help.
Nick
SCJP 1.2, OCP 9i DBA, SCWCD 1.3, SCJP 1.4 (SAI), SCJD 1.4, SCWCD 1.4 (Beta), ICED (IBM 287, IBM 484, IBM 486), SCMAD 1.0 (Beta), SCBCD 1.3, ICSD (IBM 288), ICDBA (IBM 700, IBM 701), SCDJWS, ICSD (IBM 348), OCP 10g DBA (Beta), SCJP 5.0 (Beta), SCJA 1.0 (Beta), MCP(70-270), SCBCD 5.0 (Beta), SCJP 6.0, SCEA for JEE5 (in progress)