Hi Nicole!
Welcome to the Disney Parks Moms Panel! I too love love love this uniquely Disney souvenir. (Although I'm not sure if I loved the Disney-fied pieces more than the challenge of stuffing as many as I could into a single box.) Currently the Mr. Potato Head Pick-A-Part station that you mentioned at Once Upon A Toy is not available. There is a bit of reimagining work being done around Disney Springs right now where some stores like Once Upon A Toy needed to hold options once available elsewhere. So there is a chance that this stand might come back in the future, but as of this current writing it is not there.
There are plenty of other interactive and personalized
Disney souvenir all across Walt Disney World Resort. You can customize your very own lightsaber at Tatooine Traders in Disney's Hollywood Studios or create your own cuddly creature at Build-A-Dino inside T-Rex at Disney Springs. The Japan Pavilion in Epcot's World Showcase features a tank of clams where you get to watch whichever one you picked get shucked to reveal the perfect pearl, and you can then have it set into a necklace or ring. You can even customize a Disney phone case or MagicBand at the D-Tech On Demand stall inside the Marketplace Co-Op at Disney Springs.
If you're more on the lookout for Toy Story gear then you're in luck. Walt Disney World Resort is like a giant Al's Toy Barn right now in celebration of the opening of
Toy Story Land. From popcorn buckets to ears, even specially themed cake pops and candy apples, you're sure to find hints of Buzz, Woody and the whole Round Up gang almost everywhere you look.
Do check back closer to your magical vacation, Nicole, and I'll keep my fingers crossed for the both of us that our favorite spud sets up shop once again.
~Kristen