I am an ASA and we are one of the smaller groups nationally, as is Theta Xi. One of the card stores in town got pin pillows in one time but only got them for the sororities on campus that were the bigger ones nationally.
Ask the Greek store on campus where they order their stuff from, and contact the company directly and let them know they are missing out on a big market. Plus try contacting other chapters and seeing what their situation is. Good luck!