I ask around if I haven't seen or kept them myself - there are some cichlid keepers round here who have a bunch of weird stuff. I also do a bunch of web searchs -I'd normally look at a few of the general cichlid sites, then do google searches on the scientific name. Some fish have a lot of stuff, some have next to nothing, dimerus falls somewhere in the bottom of the middle. Doing a google search on Cichlasoma dimerus gets you stuff like
/www.kcff.net/newworld/cichlasoma/dimerus/gallery.htm
Note the genus is upper case, species all lower case - unfortunately this make a difference. Read German or Dutch - this can be useful. Fortuneately most swedish aquarists publish in English. I find the web rings too hard/time consuming to search thoroughly unfortunately, though I suspect this is much of where the real info changes hands
I find fishbase almost useless. I really only look at it for original location, and max size.
There is a lot of stuff out there, both fish and articles. I got a fish last week from a dealers tank that is a wild caught cichlid from Peru. It was a contaminant with a bunch of Apistogramma 'Blue' (and what the hell is that?!'). I think it's a Burjurquina species, but this is really testing my id skills, especially as I can't find any images of these.