Odd are you wont find the correct o-rings at your local hardware store, also The dome rings are made from special material. Think its called viton? <-- spelling?
That is a pro-x /la-sleeve cylinder.. its not made by CT but.. they work on them. I believe they were originally designed by CP in a joint effort with la-sleeve. CT would be a good place to get the o-rings from. Dont bother with the hardware store plumbing rings... get the right parts and do it right the first time.