https://mocktest.aglasem.com/test-process/ailet/ailet-full/99/6706/b7451c44-5535-11e9-88e0-026373add56c#

https://toppersexam.com/paper/paper_running.php

https://www.tcyonline.com/login

To take free mock test you can go to the above links. There are number of mock test series available online which are free of cost and you just need to sign in. 

You can also buy mock test packages. Many institutions like Career Launcher and CLAT Possible provide for mock test series online which you can buy the links of which are given below. They also have different levels of mock test.

https://www.buytestseries.com/TestSeries/AILET-Single-Online-Mock-Test

https://www.clatpossible.com/our-courses/all-ndia-mock-test-series/

You can also refer to certain books for mock test series. Pearson and Lexis Nexis are some of the best books.