Here is the Facebook event.
As of this writing (9 February), there is no guarantee that we will have permission to collect signatures. Houston Peace & Justice Center has traditionally had several Green Party members on its board, but it is scrupulously non-partisan. David Rovics and members of the Deconstruction crew are sympathetic to the Green cause.
This year, Houston's largest and most Housterrific annual event runs down Smith Street Saturday 14 April. More than 100,000 Art Car fans will likely turn out for the parade.
This is an above-average event for signature-gathering. Get there early to catch people finding there vantage points, or in line at the food trucks, rather than distracting them from the parade. There should be chances to find signers after the parade as well.