You can try JCR. "Journal Citation Reports offers a systematic, objective means to critically evaluate the world's leading journals, with quantifiable, statistical information based on citation data. " : http://thomsonreuters.com/products_services/science/science_products/a-z/journal_citation_reports/
Normally, journals display their Impact Factor and CiteScore on their About Page. However, you have to be careful because predatory journals post fake Impact Factors too. Therefore, a best place to check is on SCImagojr and Thomson Reuters as suggested by previously. You can also try using SCOPUS.
scimagojr.com and webofknowledge.com gives different Q values for the same journal. In earth science for example, "Tectonophysics" is Q1 in scimagojr.com, but Q2 in webofknowledge.com. Similarly, scimagojr.com gives generally one degree higher rank for the same journal. I think webofknowledge is more accurate. If "Tectonophysics" is Q1, then, which Q value will be given to "Nature"?
In a case that you need a MS Excel file with Journal Impact factors for 2019, it is available at: https://www.sciencesoft.cn/wp-content/uploads/2019/06/Journal-Impact-factor_2019.xlsx