Hello, my name is Peter, and I am a Disney Build-A-Droid Factory-a-holic...

Just spent the week at Disney - did I really need these droids? Nope, but I couldn't NOT make a stop at the Droid Factory

A couple of these droids, were just making droids that were alternate designs I considered for my original set of 50 droids but didn't do so that I could get x-number of each part.
Tops on my to-do list were the Blue-dome R9 on the white w/blue body and the Red R3 dome on an all-red body.
The Black/Red R6 and R9 are for my desk at work and the other droids were built just to add one more droid with those parts to the collection - with the exception of domes (of which now my collection has 57; 3x of the seven domes in the pic above and 2x of the remaining 18 domes) - I now have, at a minimum, 4x of every other part in the set.
I was also able to score the Search for the Rebel Spy and Star Tours Sector 2 Security box sets while I was there as well - glad to finally add them to the collection.
I kinda lucked out - the first night we were there, we went over to Downtown Disney and I stopped into the Once Upon a Toy store - grabbed the box sets and droids.
Parts-wise, they were pretty limited, I did not see any of these parts:
Silver w/Blue R2 Dome
Silver w/Red R2 Dome
Purple R3 Dome
White w/Blue R4 Dome
Silver w/Blue R7 Dome
Blue w/Silver R8 Dome
Blue/White R7/R8 Trunk
One of the employees had to help me by going into the back and getting me a 2nd Black R6 dome (I built 2x of each droid), 2x of the White w/Purple R2 Trunks (there were NONE in the display) and the White w/Blue highlights legs I needed.
Plenty of middle legs of all colors, plenty of the hats of all styles. Green droids don't seem to be very popular, while there were plenty of Black, Blue, Red and Green legs, the most prevalent were the Green ones.
If you're heading down, I would strongly recommend trying the Downtown Disney location first since the build station has four sides and the employees are actually grateful to see someone building droids who wants to BUY them. The woman who helped me lamented the fact that over at the Lego store there are these stations where kids can build stuff - for free - and when kids come into the Once Upon a Toy Store - they often think the build-a droid and build-a-lightsaber stations work the same way. In fact even while I was building, several parents asked me "do we have to pay for this?" - meanwhile the station is plastered with the pricing signs so the first two times I was asked I politely responded "yes" and referred them to the pricing information, the third and fourth time, I simply responded "duh?!?" and the last time I said "no - I think you could walk out of here with all the parts you can carry - for free!" - the adult looked at me and knew I was giving him a smart-assed response.
When I went through Star Tours, I noticed that they have the Build Station at Tatooine Traders locked down like prison. They have the rope line and then when you go into the build station, they block it off from anyone else from standing there next to you and the whole time, there is a cast member "helping" (more like hurrying) the kid along with building his/her droids. Glad they weren't doing it like that when I was there back in May 2012.
So definitely go to Downtown Disney
FIRST and then if they couldn't help you with a specific part and you're already heading to Hollywood Studios, try the Tatooine Traders location as a rushed "last resort".