Not sure what you've already covered, but for primary sources on this you could try the archives of the Jewish Daily Forward, the New York Call, or really any of the city's newspapers. Also the ILGWU archives, the WTUL archives, or the papers of any of the strike's prominent participants and organizers: Rose Schneiderman, Pauline Newman, Clara Lemlich, Rose Pastor Stokes and I'm sure many others. Clara Lemlich also wrote a letter about the strike that was published in Jewish Currents in 1982. Also, labor activist Theresa Malkiel published a fictionalized diary of the strike in 1910.

Other contemporary Jewish labor leaders like Abraham Cahan and Morris Hilquit both produced many books and pamphlets around the time of the strike. You could also look at the minutes of the Socialist Party of America.

For a jumping off point for this I'm using the bibliography of Greater Gotham: A History of New York City from 1898 to 1919 by Mike Wallace which covers this and several other of the city's strikes pretty extensively. I'm by no means an expert on the Shirtwaist Strike, but while reading on related topics I have found Wallace's bibliography to be a gold mine.

Here are some secondary sources I plucked from Wallace that directly address the strike. These books' bibliographies themselves list a ton of primary sources on the matter. Most of these have free previews available online.

• All Together Different: Yiddish Socialists, Garment Workers, and the Labor Roots of Multiculturalism by Daniel Katz (2011)
• The Triangle Fire, Protocols Of Peace: And Industrial Democracy In Progressive Era New York by Richard Greenwald (2005)
• Cultures of Opposition: Jewish Immigrant Workers, New York City, 1881–1905 by Hadassa Kosak (2000)
• Women and the American Labor Movement by Philip S. Foner (1979)