Practically any community college with a nursing department will offer CNA training... contact the continuing education departments and they will let you know...
Lone Star College (old name North Harris Montgomery Community College)
with locations in Kingwood, off of 1960, The Woodlands area, Tomball, CyFair)
San Jacinto college- locations near Clear Lake, Pasadena, North Shore areas
Houston Community Colleges, with locations near the medical center and all over Houston
Just do a web search for these schools
and then go to the appropriate page on the site. Pick up a phone and give them a call. There are programs all over Houston starting at various times in the year.