The two Anglo-American periodical indexes Index to Legal Periodicals (ILP), and LegalTrac are worth checking, because articles sometimes provide comparisons with foreign legal systems or address international tax.
Index to Foreign Legal Periodicals (IFLP) indexes primarily non-English-language law journals, using English subject headings.
Tax Management International Journal
Tax Notes International (Arlington, VA: Tax Analysts, 1989- ) (PER.T361). Also on LexisNexis Academic and LexisAdvance.