Borderlands custom map links
Here’s all the individual custom map links I can find for Borderlands 1.
Most of them come with instructions on how to put the files in the right place but ask if it's not clear.
Note that if you exit most of these maps part way through, you'll have to start the mission again from the beginning.
You need the Oasis map hub to use all of these (see Mapslot 6 in list below).
Note that because I wanted to keep this list 'clean' I've included working links to mapslots with useable content only
EDIT: I recently (Nov '15) realised it's still possible to access the old forums, so you can actually find the complete list of map hubs, links and importantly discussion about how far these projects got, here: some of the links are broken though whereas all the links i have listed separately in my post below are working: http://oldforums.gearboxsoftware.com/oldforums/20150308085538/http://oldforums.gearboxsoftware.com/showthread.php?t=108800
Prior to discovering the above old forum link, I put up a companion post to this which just for the record lists all of the custom map projects, including those with no working link or which were unfinished. I'll leave it up in case the old forums go down again: http://forums.gearboxsoftware.com/t/borderlands-1-original-list-of-mapslots-reservations-etc-no-links/527314
Hope this is helpful - do ask me to add any more maps you have or any updated map versions - keep B1 alive!
Complete Download: xDORSx, another forum user, has kindly created a map pack with everything in it as one download - This includes some maps i don't have individual links for, so if you're starting from scratch this is probably a good bet...: http://steamcommunity.com/sharedfiles/filedetails/?id=507827284
I'll still keep this list of individual links going though, and if anyone wants to give individual links for ones where it's in a pack or have updates etc do let me have them
Sources of several maps
Some of the maps are amalgamated at common sites:
Individual Links with Oasis Mapslots: