@375Fox has pretty much nailed it. For instance, in the Zambezi Delta of Mozambique only a limited number of Coutadas have buffalo. The quota is quite large, so a number of other operators purchase quota based on their number of clients for the year. I know at least two, who charge client a trophy fee that is less than the actual cost of the tag. I business plan accounts for that discount trough trophy fees outside the buffalo concession and the daily rate. Those two outfitters could arrange a second buffalo, but would almost certainly have to charge full cost for the second tag.
Other than Tanzania, the most likely place to arrange a second bull would probably be a South African game ranch operation. I suspect several outfitters here would make you an offer. I would also assume they would be looking for a ten-day to two-week commitment and again, likely a premium on the second animal.