Five Critical Period papers by Patkowski can be found here:
2013: “The Critical Period and Parameter Setting in Five Cases of Delayed L1 Acquisition.” EUROSLA Yearbook, 13, 1-21.
2003: “Laterality Effects in Multilinguals during Speech Production under the Concurrent TaskParadigm: Another Test of the Age of Acquisition Hypothesis.” IRAL: International Review of Applied Linguistics in Language Teaching, 41 (3), 175-200.
1994: "The Critical Age Hypothesis and Interlanguage Phonology." In M. Yavas (Ed.), First and Second Language Phonology, 205-221. Singular Publishing Group: San Diego, CA.
1990: "Age and Accent in a Second Language: A Reply to James Emil Flege." Applied Linguistics, 11 (1), 73-89.
1980: "The Sensitive Period for the Acquisition of Syntax in a Second Language." Language Learning, 30 (2), 449-468.
A sixth paper is accessible from ERIC:
2014: "Looking for Structure: Is the Two-word Stage of Language Development in Apes and Human Children the Same or Different?" Studies in Second Language Learning and Teaching, 4 (3), 507-528.
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