I’ve done some searches and checked the sticky regarding, them… Every website that people claim to buy them from, does not list them only for sale. I’ve got plenty of black inserts and extra power extractor springs, but I’m down to my last O-ring.
Thank-you
Matt
I bought some from Rainier Arms just a few weeks ago. I had to pick up my upper from them after having the flash hider pinned since they are local and got 3 to try out on my personal rifles. I’m not sure if they have them on their website though. Thay had a bunch of them.
You can get them from bravocompany.com but if you aren’t having any extraction problems you DO NOT need them. If you have spare inserts and springs, you’ll likely never need the o-ring.
I called McMaster (supply?). I’ve still got the receipt somewhere. Anyway, I called them and spoke with them. After determining that they sold many of these to various firearms vendors and manufacturers I ordered a hundred pack for around $10.00. If you send me a PM I’ll chase down the receipt and give you the parts number or send me your address and I’ll send you a dozen or so as I’ve got a lifetime supply as I don’t generally use them.
The website is www.mscdirect.com and the item number is 09265067.
They are $8.73 ea for a 100 pack.
McMaster Carr was the other vendor. $4.82 for a pack of 50 o-rings:
Thank-you all for the replies. Sounds like I can order them for much cheaper through a non-firearm supply house.
Seb5, thank-you for the generous offer! Hold onto them, if your experiences mirror mine, you’ll give them away at the range and training more than you will ever use.
Matt
Good to know
There’s probably several stuck to the bottom of my trash can. 
There #60 o-rings. You can get a pack of 10 at Lowes or Home Depot in the plumbing isle.
Can you use an o-ring to extend the life of a worn extractor spring?
Hardware store o-rings aren’t usually Viton rubber which resists attacking from chemicals and oil. Viton o-rings last much longer than hardware store rubber o-rings.
Another tip:
This same size o-ring for AR extractors works well for keeping 1911 grips screws tight as well. I use them between the grip screws and grips on both of my 1911s.
You’re absolutely right about the Viton, not the same animal. And I like the grip screw idea… Thanks!