O-ring type question

The 3x3 reference sounds like you're dealing with a metric O-ring. "Inch" sized O-rings are called out with a dash reference like -113 (dash one thirteen). So the 3 x 3 would mean a 3mm cross-section (thickness) and a 3mm inside diameter. That means the outside diameter would measure 9mm. BTW that example describes a chubby O-ring...proportions unlike anything I've encountered in my dealings with AGs.

Normally there would be a letter M preceding it like this example:
https://www.amazon.com/M3x10-Viton-Ring-Durometer-Round/dp/B00NJPOQ9E

I can't answer the second part

Here is a link to The O ring Store and the O ring you are looking for. https://www.theoringstore.com/store/index.php?main_page=index&cPath=368_12_46&sort=2a

Yes, shipping is $8 but you can buy a whole bunch of different O rings (like hundreds of them) and the shipping will not change. For instance you could order some O rings for your female Foster coupler (size 010) that are literally 1 cent per piece with a minimum buy of 100 and give them away to all of your airgunning buddies!

Ragu,

Not at all, I am a Lightning owner so I like to think of you as genius X genius! Thanks!

If you go to the link I posted for the O ring store, they have a ton of good information on O ring sizing convention and also all the different O ring materials. If you spend 30 or so minutes reading through the info on their site you will be an O ring genius in no time. And you can't beat their prices and service. I ordered every single O ring that my Veteran 22 uses, most of them were minimum buy quantity of 20 for a total of right at 300 O rings total. Total cost including shipping was $21.59 and I had them in 2 days (from Washington state to Florida). You can't beat that!

Chip