That looks exactly like the fitting and washer on my Milwaukee MA957 regulator. Go to this web page:
http://www.milwaukeetesters.com/co2regulator.html
click on the "contact" button on the upper left, and send an email to the "support" email address. Tell them you need to get some new nylon washers for your regulator. They sent me 2 for free, and I know of others that have done the same thing. I don't know of anyone who sells them. You could replace the nipple with a standard CGA-320, if you could get the old one loose. There are many places on the internet that sell them.
http://www.milwaukeetesters.com/co2regulator.html
click on the "contact" button on the upper left, and send an email to the "support" email address. Tell them you need to get some new nylon washers for your regulator. They sent me 2 for free, and I know of others that have done the same thing. I don't know of anyone who sells them. You could replace the nipple with a standard CGA-320, if you could get the old one loose. There are many places on the internet that sell them.