Unless you plan to use the same travel agent to book the adult tickets, I can't imagine that any travel agents would be very interested in this business. I'm also unsure how easy it is to find a travel agent who really understands the infant ticket rules for different airlines and routes. You might need to figure out exactly how each ticket should be done and then feed this information to a travel agent rather than using their advice. If so, why can't you similarly call the airline and direct them how to do the infant ticket--unless the airline is one that encourages passengers to purchase infant tickets at the airport on the day of departure. [If the airline requires paper tickets for the baby, be aware that travel agents might impose additional fees for this, even if you go to the travel agent's office in person to collect the ticket when it's ready.]