We have wooden chairs in our porch that need reinforcement because the
cushions are starting to sink down into because some of the pieces
holding up the cushion under the seat have fallen off and gotten lost
over the years. I am bad at describing things because i am not that
mechanically inclined, but when you take the cushion off and look down
at the seat, there are a total of four metal rods/bars (whatever)
crisscrossing each other forming a tic-tac-toe board held to the wood
by hooks with springs on them. On some of the chairs the hooks/springs
have been lost and on some of them one or more of the metal supports
have been lost. I have tried bungie cords but they wear out quickly.

Does anyone know if there is a website or store that sells replacement
parts, and if not, if there are any other ideas to support these
cushions?