Well, chains are simple to get. Go to an engineering firm, or good hardware store nad make up your own set.
For bands, you have a few choices. You can buy from elitefitness, which costs an absolute fortune (full set at 155$US = ~260$NZ+ postage)
Or you can do what I have done, I will probably get some pictures set up at some point but I will explain for hte moment.
I got a few pieces of nylon webbing about 25mm wide, adn got my wife to sew in some metal D rings. (4 to be exact). This will provide attachment on the rack/bench and the bar at the top. Then I brougth a pack or two of bungy cords from the warehouse which I use to connect the straps top and bottom.
Dont know the resistance, but it doesnt matter for how I train, it just helps. (and it didnt cost me 260$+ or just under 2 weeks rent where I live at the moment…or about 1days rent if you live in Ak
I also got my wife to make up some nylon ‘slippers’ to fit over my arms to make putting the bench shirt on really really easy. My wife didnt even struggle to put on my loose shirt, which was trouble for her to do (even when I was 10kg lighter…)