to a site selling a dog pram/stroller:
there are some interesting items at theis site also:
It seems that you could use some strollers made for human babies by making some creative additions. 6 years ago when our dog became paraplegic and before we could find a cart for her (it was hard to locate one in those days), we used a heavy duty child's wagon to take Roxy for walks. I fashioned a removable three sided "box" which slipped into brackets on the sides and rear of the wagon - this supported Roxy in a sitting position and kept her from falling. It worked well. She was a large dog and a pram/ stroller wouldn't have worked.
Here's Roxy in her wagon: