The OP is not using #6 shot, He's using #9 shot. The #6 was a load number reference.The larger the shot size the less a MEC bar will drop by weight because of more air space between each pellet, it just can not pack as tight.
The only other source I know of is Precision Reloading, but they won't be any less expensive.I'll give it a try. Ballistic Products wants $20 for 500 wads, plus $12 for shipping. Can you suggest another online site? I'm in NY and we have nothing in the stores.