you unfortunately are not going to find an inclusive list that tells the max sizes. Planetcatfish allows you to search for fish that are similar in size but that is about it.
There is a great deal of discrepancy between all of the sites as to the max sizes of many fish. You must also take into consideration that the "max sizes" are averages of fish, so you may end up with an inch or so here and there.
As to what can live in a 125 for its entire lifetime
4-line cat
School of pictus
Mystus castaneus
Mystus Vittatus
Bumblebee cat
Tons of synodontus
There are even different pims that could do it.
Sun cat
Spotted raphael
Striped raphael
As to how well these will coexist with your cichlids, its hard to say i dont have any experience with either, but this is a start for you, if i was near my books i could list better, but this is basically off the top of my head.
Good luck
PS. my personal favorite catfish sites are
Scotcat.com
Planetcatfish.com
fishbase.org
aqualandpetsplus.com (this is nice for the more common fish in the hobby)
also aquariumlife.net and fishprofiles.com entertain me but are very limited on fish.