The winches are pretty standard items, have a look on eBay, you'll find lots. It's mainly a case of getting the mounting dimensions right, strop winches of that size should all be the same loading.

Don't get one with a cable! I did once as I thought it would avoid the problem of wear on the strop, but it was a nightmare with the cable springing around when loose. I ended up buying a strop and replacing the cable.