Yeah it's a tough question because I suspect it varies pretty wildly by region. When *everything* but the base game and big ships were impossible to find I was cherry picking Barnes and Nobles in my area grabbing ships they had in stock. For a while there the plain old TIE was the hardest one to find and at one point I had to buy a second core set just to get a couple more.
For quite a while, the A-Wing and Interceptor were definitely the rarest, but then there was a big wave 2 restock a month or so ago and while they sold out in a week, everyone was able to get their hands on more of those at the time. It's possible the Y-Wing is now hard to track down - I haven't looked, because I already have 3 or 4 - but for the longest time I thought I was the only person in the country who WANTED a Y-Wing, so... ![]()