John,
I use Paterson tanks and that requires 500ml of mixed developer for each 120 film. With Rodinal at 1+50 you'll need a minimum of 10 ml of concentrate for each film = 20 ml in all. Rodinal is as far as I know strictly a one-shot developer and based on the small recommended quantity of concentrate it is almost certain that it will be close to the point of exhaustion when the film is developed. So it's not a good idea to try running a second film through it, even at lengthened times. I'd recommend getting some more developer!
Photo Continental in Brisbane don't show any chemicals on they website but it might be worth a call as they're local to you.
Les Porter Photography is showing Ilford Chemicals in his price list and he's certainly worth talking to - he usually has some stock and a very good next day Express delivery through Australia Post. Ilfotec LC29 can be reused in the same processing session if mixed at dilutions of 1+9 or 1+19, but not at the higher dilution of 1+29.
Or you could get a packet of ID-11 but if you're not using much it's not worth it as the stock solution will "go off" after a month or two thus negating the apparent savings over the liquid developers. But you can use ID-11 stock solution more than once by pouring the used developer back into the stock solution bottle, then measuring out the quantity (500ml) for the second film and adding 10% to the time for the second film (due to the "mix" not being as potent as the original stock solution). Then discard it.
