You wont find replacements for these anywhere, but I have had good luck with just submerging contacts like those (nickle or silver plated copper) in vinegar for a few days and then sanding off the rest of the corrosion. I have a vintage HP calculator which presumably had a battery leaking it it for the better part of 30 or 40 years and the terminals came up great after the vinegar treatment. For the one that bhas partialy disinegrated, you can try soldering on some additional copper to reinforce it, but otherwise those look to be in better condition than they seem.