First of all, I know it's random. Personally, it does not make sense that the flirtations are somehow special and has a lower rate of people getting them. Doesn't change the fact that the incubus flirtations only has two in shops currently. Even the more popular items that have been given out by GOFP has been deflating. I don't see why it would not happen with the flirtations as well. Are you really sure your friend got one?
I'm checking into this right now. I've been busy the past few days and just received the mail you were talking about, . If these trunks are indeed missing from the bag then they will show up soon. :)
As a message for everyone please make tickets for these sort of things. I will most likely reply to a ticket quicker than smail (due to some real crazies mailing me, haha).
[edit]
These trunks can now be found in the GOFP. :)