Tm99

Hi guys. I'm new on here although been reading along for some time now.
I have two old Super Nitro RS4's (with the belt drives, which i believe are also called 2nd generation model).
they have been sitting collecting dust for about 8 years and now i want to get them up and running for my children but need a couple of rear diffs (A430).
unfortunately, this part has been discontinued by HPI and they don't specify an alternate part. I've looked everywhere!
Does anyone here know which other part will fit? I think it's 39 teeth so i would want to keep the same so i don't have to change belts, etc which will only add to the expense.
Thanks in advance guys. Your help will be much appreciated.