For the Convention Center, try 154.8600 and 153.9350 (license KFN595). Also try 855.5125 and 858.2375 (WPEB486). For the Sands Expo Center, I found four licenses: WNVC418, WPLY951, WPPV380, and WPTW653. There was also a license for GES Exposition Services (probably does work at the Sands) for some 935-940 band frequencies, but I can't find it in the FCC database now. I'd search this band, looking for an LTR system. For the Alexis Park, check out WQDZ413. Hope this helps, and let us know what you find.
Dave