Here are some useful links to on-line resources for Nicaraguan archaeology:
http://www.granadacollection.org/
This links to a fine web page for Mi Museo, a private museum in Granada, Nicaragua with abundant on-line images and descriptions of pre-Columbian pottery. Mi Museo also publishes the only journal dedicated to Nicaraguan archaeology, in both hard-copy and electronic media.
http://www.peabody.harvard.edu/col/
The Peabody museum has an on-line collection of objects collected in the late-19th century by Earl Flint, including numerous complete vessels from the site of Tola in the Rivas region.