Need load-o-matic distributor part - where to get???

I believe the diaphragm on my stock distributor has a hole/tear in it. When i have the part out and i press on the post there is air that comes out of the port where the vacuum line from the carb screws in. When i put my finger over the port and press on the post the diaphragm doesn't hold suction; it returns to normal. I believe the diaphragm should stay put if i push or pull the post and place my finger over the port hole. It doesn't do this. I can pull and push the post with my finger over the port and air whooshes in and out. Where can i get a replacement diaphragm for the stock load-o-matic??? thanks

Any auto parts store, napa oreillys ect

http://www.oreillyauto.com/site/c/search/Distributor+Vacuum+Advance/02818/C0334.oap?model=Econoline&vi=1333796&year=1964&make=Ford

I literally just bought one earlier today from advanced auto for about 24 bucks.