Hello Neil, there would be a lot of time and money involved making new track frames from scratch, I'm really surprised you are struggling to find a decent pair over there considering how many D2 tractors were made, there must be thousands of them still laying around farms worn out or busted, though I know you are looking for the later model extended frames.

My advice is put a advert in the ACMOC magazine for the parts you need, hopefully someone over on the drier west coast has a wreck they will sell you, and in the meantime find a nice cheap 22 to play with while you keep your eyes open for the D2 track frames and undercarriage parts you need. From my experience, you end up spending a lot more money than we should, saving a old Cat when you rush the job, buying the first parts you see or get offered, not matter what they cost, because it's very easy to spend $10,000 on a old Cat that at the end of the day, is only worth $4,000 sadly.

Your D2 restoration has been a real challenge hasn't it, but you reach a point of no return with a lot of time and money invested, that you have to continue the project, still, I suspect you are like me, we are not doing it with the goal of selling Cats to make money, we are doing it because we love the challenge of saving our old history, our wives will inherit the unfinished projects we leave behind! LOL
All the best
Mike.