Conroe Swap Meet is a 3 day affair at the Montgomery County Fairgrounds. It is the largest swap meet in the area, with mostly used auto parts. There are numerous vendors selling new parts, new tools and a few selling automotive related items, such as model cars, etc. There is also a car corral. There is plenty of free parking on the grass in an adjacent field.
The obvious question is how much petro stuff is there. It varies, but there is usually a vendor there with artificially aged signs, etc. There are usually several scattered vendors with authentic petro and soda items, but it's hit or miss. There is usually a vendor selling restored petro and soda items. He's a real nice fellow and will work with you on price.