Hi Mark, I don't do much SPANISH music except for some flamenco stuff from the Gypsy Kings - on wait, they're actually French
Anyways, I do cover lots of LATIN music (Cumbia, Salsa, Merengue, Bachata, Reggaeton, Nortena...) You can go to my website and here some arranger bassed Latin music. My website is listed in my profile. Also I could try to email you our song list. I think my wife made one...
Regarding sheet music: I haven't found much for the more modern dance stuff. I had to learn most by ear and my ears suck! If I can do it, anybody can. Luckly the modern stuff doesn't have a lot of chords changes. Also you can search on google for lyrics and chords. Type the name of the song followed "letras y acordes" Just be ready to make some corrections- lots of mistakes!
Oh, I just remembered there is a magazine that I pick up when I'm in Mexico. It's called "Teclado Facil" It does have some lead lines written out and chords and lyrics. It's pretty good...
I'm not sure if they are on line- maybe do a search.
Another thing, alot of those slow boleros that you allready do can work as salsa or menergue.