The only thing really "specific" about it is the way it's bent, but yea still widely available. I was just going to swap it for the one in my LT, it's only a few years old, but it also has a crack in the tube. So I grabbed the Dorman one from Amazon for $10 - the same one they have at Advance, Autozone, & O'Reilly for $30.

I'm thinking about replacing it in both cars with 316 stainless steel, & never have to worry about it cracking / breaking again! 316 is the most resistant to gasses from lead acid batteries. 8mm OD 316 stainless tubing coil would be nearly perfect, & I should be able to find a stainless fitting to fit the battery as well, or I could epoxy the plastic elbow to the stainless... The tubing is $17 for four 30cm pieces, & just need to bend to shape. It's slightly smaller diameter than the exhaust hole, so a little silicone around it will keep any gasses from being blown back inside!

 

The tube is not bent, there is a 90 degree adapter that seals into the hole in the battery. Bending a piece of tube and stuffing it into the battery is no the same.
I wonder how I am still alive after driving air cooled VWs for 15 years, with unvented batteries under the back seat. I choose to not spend my angst on things like that.

You could probably wander around a battery display and surreptitiously acquire one from a battery. There are several sizes that utilize vent tubes.

 

My MGB’s had two 6 volt batteries under a tray behind the seats, no problem!

 

What??? NO, I'm not pilfering something I can buy of Amazon for less than $10.

BTW.... all 4 battery tubes I've run across in my HHR's were this tube below:


It's a rigid plastic tube with two bends in it. BTW, 2010 LT had an AC Delco battery and this tube in it when I bought it. That battery was then replaced with an AC Delco battery, which also came with this tube... so that has been the extent of my knowledge for the HHR battery tube, If there's a different one, I don't know about it.

 

Nope no different tube from GM