Where can i find i find O-rings

Call them.

Did you ever find out if you needed and O-ring? I too have a pro circuit.

There should be 2. Just like on a bike.

I don't think the pro circuit does. There aren't any slots where an o-ring would sit.

Not sure about pro circuit, but the Toomey pipe and flange uses a #223 high temp (red) silicone O-ring.
Which fits what i believe is a standard header flange. As to whether or not the pro circuit pipe has a slot machined for the oring to fit in, I cannot say.

If you need the O-ring oringsandmore on ebay (also at oringsandmore.com) has a 15 pack for around 50 cents a piece shipped.
I ordered from there and 2 or 3 days later the orings showed up, quality looked as good as any and they fit just right.
Pretty good deal if you ask me.