Ah, looks like ThinkGeek doesn’t sell it anymore. But this is the same coat, from the original source (AbbyShot–they make lots of very nice replica Who stuff). Again, though, quite pricey:
I got my coat at Goodwill, but a trenchcoat/duster in a child size could be tricky to find. The suit, I bought online at a discount men’s suits place. Not a perfect match, thanks to the customizations the show’s tailors made, but good enough for me.