Borrowed chords can be any parallel named chord: i.e. they can come from any scale as long as they use the same naming note. E.G. If you have G major you can use G minor or G diminished or G augmented and vice versa.
Because the borrowed chords will not contain scale tones, you need to alter your melodic material to match, e.g. you have borrowed C minor so you must change any E's to Eb unless you have the E as part of upward or downward chromatic scale run.
You can also substitute other chords for the original chord in your progression:
1) using elisive susbtitutions:
vi - I - iii form a trifecta of related chords: they use notes 613 - 135 - 357
ii - IV - vi form another trifecta: 246 - 461 - 613
iii - V- vii form yet another trifecta: 357 - 572 - 724
2) use the diminished 7th one semi-tone up from the major chord:
V7 becomes #v7b5 ~ GBDF -> G#BDF ~ 1-3-5-b7 -> 1-b3-b5-bb7 (chord tone numbers)
3) tritone substitution:
in the progression
iii-vi-ii-V7-I ~ Em-Am-Dm-G7-C ~ EGB-ACE-DFA-GBDF-CEG
[MP3]http://www.bandcoach.org/fp/audio/chordSubs01.mp3[/MP3]
we instead use
iii-bIII-ii-bII7-I ~ Em-Eb-Dm-Db7-C ~ EGB-EbGBb-DFA-DbFAbCb-CEG
[MP3]http://www.bandcoach.org/fp/audio/chordSubs02.mp3[/MP3]
4) Secondary Dominants
in the progression
iii-vi-ii-V7-I ~ Em-Am-Dm-G7-C ~ EGB-ACE-DFA-GBDF-CEG
[MP3]http://www.bandcoach.org/fp/audio/chordSubs01.mp3[/MP3]
we instead use
V7/vi-V7/ii-V7/V-V7-I ~ E-A-D-G7-C ~ EG#BD-AC#EG-DF#AC-GBDF-CEG
[MP3]http://www.bandcoach.org/fp/audio/chordSubs03.mp3[/MP3]
you should also check out this post
https://www.futureproducers.com/for...t-key-scales-chords-help-361875/#post49097376
