where can I get a new wheel for my wheel barrow

It might sound TOO obvious, but try your local tyre distributer, particularly if he is an independant. I asked and they had a new tyre for me in a couple of days and it was much less expensive than I had expected.

You could also try a small engine or lawn and garden equipment repair shop. We have, or can get, tires of that size as well as tire tubes. I just fixed one today.