That would probably not be a legit "roll bar",it's more likely a "show bar" that is meant to hold lights more than anything..though I have seen a few that were real roll bars,that also had a platform you could bolt a small winch onto,to pull heavy items into your truck's bed..
I have seen a bar like yours in a local boneyard,in an old Dodge stepside pickup..probably no better shape than yours,and it might not be there any more--things dissapearing fast now that scrap prices are high..
I last saw one like yours for sale at Thompson Speedway's swap meet--in fact,someone LEFT it near piles of other stuff near the trash cans!--I was tempted to grab it,but my stepside has a toolbox,my bed is 8' long,but adding that bar AND a toolbox would leave about 4 feet of useable bed space!..so I left it there--and it was in nice shape too--so was the antique "Clinton" horizontal shaft engine someone left in the scrap pile,complete down to its air cleaner..had I not been exhausted, and parked 1/2 mile away,I'd have taken both home with me!..
I'd say JC Whitney still has them--might ask at "Pep Boys" too--they seem to be able to get more "add on" accessories than most any other store around this area..a place in Fall River called "Tuff-Stuff" used to carry them( a 4x4 speed shop of sorts)--but its been years since I bought anything there--not sure if they are still in bussiness or not.."Yankee Custom" is another place you might try too..