You can try using the store finder functionality on Game Stop's product page.
http://www.gamestop.com/accessories/pokemon-go-plus/131550
Supplies are very limited, maybe 2 or 3 units per location. If you wanted to save the hassle and order online, coupon code "saver" will give you free 4-7 day shipping.
UPDATE: Amazon now has it. https://www.amazon.com/gp/product/B01H482N6E/
I don't think that's Walmart. Looks like a third party site that is using Walmart's formatting in a deceptive way.
This is the real site:
https://www.walmart.com/ip/Pokemon-GO-Plus-Nintendo-Wii-U/54200248
It is listed at $34.99 and sold out at the time I posted this.
Thanks for the explanation. It seems then that the Burmy's cloak is largely dictated by the color on OSM where it appears (green=plant, yellow=sandy, grey=trash). Though where it gets unclear is in situations like the following shopping center, where I have seen both plant and trash cloaks, sometimes even at the same spawnpoint.
For the last couple of days, I've just been putting my phone into hotspot mode, and using my cheap three year old lenovo tablet with wifi. It actually runs the game surprisingly well, and I get at least five to six hours of screen time out of it when the brightness is set 25% or lower. That's perfect since I go out at night anyway. This combination of phone and tablet means I don't need to carry any spare batteries. I also find that my aim is better with the tablet.