All the factory mounting points are there on the front subframe and lower A-arms, even if the car did not come with a bar. Restoration suppliers can provide stock parts, the aftermarket suspension kit suppliers usually will have some sort of stiffer than stock improved handling type kits too.
Since the '68-74 Nova front subframe and suspension is the same as '67-69 Camaro/Firebird, there are a ton of replacement and aftermarket kit options....here is one off just a quick easy Ebay search.:
This is a 1" bar, it will be a little stiffer than a stock bar which was 13/16" IIRC.
My 68 having an original 6 cylinder in it did not have a factory sway bar BUT the frame has holes in it for the sway bar bushing straps and the lower control arms also have the holes in them for the sway bar link ends.
With the right parts I can bolt one right into my car.