Can't see there being a shortage this year, all of the "real" supporters should easily get a ticket.
I'm not sure what the average attendance for each of the FA Cup semi-finalists is, but I'm pretty sure that Barnsley, West Brom and Cardiff (and possibly Pompey too?) all average considerably less than 35,000, which I think is the allocation that each finalist club gets.
On this basis, it could be argued that too many tickets are going to each club this year, as they don't have 35,000 "real supporters" and not enough are being distributed via member clubs and leagues so that footy fans all over the country have the opportunity to attend the season's hallmark match?!!!