jt used to sell replacement foam but those days are over.
if you are using rare frames you can buy normal frames and just use it as a foam donor by cutting out the foam from those frames and putting it on the rare frames.
if youre not using really rare or expensive frames you might as well just buy new frames.
you can also use weather stripping or empires foam kit but i dont really recommend that since nothing matches the amazingness of stock jt foam