Need O ring help

I blew the breech seal O ring out of my Brocock Bantam Sniper. 

The AOA repair sight shows how to replace and I’m comfortable doing that BUT I have no clue how to source a replacement O ring and so far no help from the locals

AOA calls for a 5mm x 1.5 (70) and I know the 70 relates to hardness the 1.5 to thickness everything I’ve seen has a ID and OD dimension and nothing about hardness. 

Can any one point my sorry self in the right direction. I’d like to source this locally but seems that might be difficult?

Thanks in advance. John Heckman 
 
i was gonna mention mccaster-karr , too. the only place i know to get some airgun parts that crosman doesnt carry anymore. they have good customer support, too. they tripped when i said i was using the parts for airguns. "we dont make airgun parts." duane from sun optics taught me about mccaster-karr. God rest his soul. i wonder if sun optics will have a table at the airgun show here on the 22nd ? maybe the new owners will do it. - paul.
 
Darned if I didn’t get lucky. They sent two extra with the gun. I had this faint recollection so after much searching for the box I was able to but the gun back in service.

That kind of luck doesn’t happen often I have another form member coming to shoot with me tomorrow and I know he was specifically interested in shooting this Brocock. So now he will be able to .