Where to buy geared diff for tlr22-2 1.0

[ChrisCorbett]

Yes I know it's a vintage vehicle (not being the 2.0) but it was £100 so couldn't resist it. For my level of skill it will be more than adequate.
I want to buy a gear diff but can't seem to find them anywhere for sale, any ideas where I source one from?

Also I am having a nightmare getting rear hub drive pin into the hole of drive shaft. It's fine when the washer isn't fitted but once I fit that I can only see the tiniest bit of the hole. I have checked the bearings are seared fully in upright and still can't get it to fit. Any tips?
Got one side in!