Yeah, mine are inconsistent too, depends on the weather if they decide to hold the hood or not. I wind up using a snow brush- A much cheaper solution
I know NAPA sells them; any auto-parts store will have those struts as they are universal in design. pmesfun is right, they typically are under 20 dollars each, depending on length.
Also in order to remove the strut there is a metal clip on each "ball end" which holds it to the stud. pop that out with a small screw driver and with a small bump, should free itself from the stud.