First, it depends on how many alliance routes are allowed. I believe the options are 0, 5, 10, 15 and 20. If it's 0, then, obviously, no one can make alliance routes from other alliance members' airports. It should also be noted that the number is the number of alliance routes allowed at each hub amongst ALL members, not per airline.
If it's not 0, then you need to look at the Alliance page. It lists the available alliance bases and a number. If the number next to the base is equal to the number of allowable alliance routes, that means no alliance routes are available to be created.
