I Googled Rupert Bear and going by the pictures I saw I would think you could use almost any bear design and just match the colours. I saw white ones and yellow ones and all looked pretty normal not like Pooh Bear.
Please do not use any bear design and make it look like a Rupert bear. You would be breaking the copyright laws and in trouble of a lawsuit.
Rupert Bear is a copyrighted design and I don't know who has bought a license to digitise it. Licenses usually don't come cheap, so finding a freebie might be unlikely. I hope someone can point you to a site.
we did think about the copyright etc which explains why he is hard to find but I'll keep looking for her.
Irene