Perfectly feasible to put inner tubes inside the leaking chambers. We do what we call an emergency bladder which is made in one size to suit most sizes of air chambers. It is made from a welded PU film, which is very flexible and when inserted in the chamber and inflated, will expand and fill all the voids. The bladder has a C7 valve and will last for a reasonable period of time, certainly give you a few years of use. Just have to cut a small hole in the tube , insert the bladder, with the valve accesible, glue a patch around the hole, which does not have to be air tight of course and inflate the bladder. Works well for both straight air chambers as well as the bow chamber.
Available to order here Emergency bladder - Henshaw Inflatables Ltd
Alternatively of course you could have a new tube made. Likely cost would be in the region of £2,800.00 excluding freight. That price would be for the basic tube in 1300gsm(1100Dtex) Hypalon coated fabric with a fitting kit including strake, handles, fitting fabric and lifeline patches and line. The only drawback is that you would have to ship either the Port or Starboard sides of the old tubes back to copy. The price of Aus $14,000 seems to be ridiculous in the extreme. Time to open an Australin branch I think!!!