Doubt you will get direct replacements. Choices are flexible tans or solid either stainless or plastic. As suggested Tek Tanks will make custom tanks for you. You may want to investigate getting the existing tanks repaired when you get the quotes for new ones.
If the existing tank is too big to get out in one piece how about fitting a flexible tank inside the old rigid tank? Should fairly easy to cut a hole in the top of the existing tank big enough to squash through a deflated flexible tank.
Remove the existing skin fittings on the old tank and remake the hoses through the old holes to join up with the new flexible tank. Probably a cheaper and easier solution than having a new tank made.