I am doing the same thing. I have 13 complete so far... there is a spot from level 17 to 21 where it seems the Massage and the Police girls show up. I get to 17 by Tuesday then I try to stay under level 21 (by losing a few matches) til Friday. This gets me at least 2 of the 'rare' girls per week.
About if they are beatable... I found a Alice with stats in the 400k area. based on that, I think the FL-team has seeded a few of the rare girls in that range.
good luck!