There are two primary places to acquire mods for BL2 and TPS: Github and Nexus Mods. Github has been the primary place to store mods for some time now, but more modders have been using Nexus recently.
Mods for both BL2 and TPS are stored at the BLCMods Github page.
When you browse to a mod file you want to download, it will either have a
Raw button or a
Download button, in the upper right hand corner of the
Right-click on that button and choose
Save Link As... to save the file to
your computer, and then use BLCMM to import the mod.
Sorted Github mods at the ModCabinet Wiki
The ModCabinet wiki is a place where github mods get sorted out into categories and gives you a much nicer way to browse through the mods to see what’s there. You can find the ModCabinet wiki here.
Historically, the ModCabinet wiki wasn’t very well populated, since users had to edit it manually to get mods in there, but on July 19, 2019, it was updated with an automatic generation process which brings in the whole github repo. If you’ve looked at the wik in the past and been underwhelmed, give it another look!
Downloading and finding mods on Nexus is more straightforward than on Github, though you do need an account on Nexus in order to download mods.