No manufacturer's currently. IMO it's pretty rigid up front. Mine is lowered and I put it through the paces regularly - don't feel much flex at all.
Location will be a deal breaker for any strut tower brace in the HHR. The MASSIVE air cleaner cover prohibits a straight across route. Also, the firewall is set back quite a bit making triangulation tricky. Location of the fusebox, brake reservoir, and AC hardlines make the task increasingly difficult.
Someone may attempt one; but a) it's not needed, and b) it's gonna be pretty funky looking to get around everything!
I agree, I had to do a quick lane change the other morning. Cruise control set at 79 and out of nowhere was a huge piece of truck tire. swerved to the other lane without hitting the brake. Just a little tire squeal but no loss of control. felt real steady. (Thank God)