I posted this tip on how to find Walmart's Exclusive TBS 6-Inch Stormtrooper (Mimban) figure on our Facebook page about 3 days ago and it worked for me today.
As most of you know, Brickseek is no help on these currently because Walmart's inventory system mixes the Stormtrooper Mimban SKU 667662952 in with the Basic Black Series 6-Inch figure SKU and always shows a zero count.
But here is a tip. Use Brickseek to check your local stores current quantities of The Black Series Basic assortment using SKU# 45057862. Make sure to note the current count. Check The Black Series Basic assortment using SKU# 45057862 again the next day (found evening / night to be best times for updates) and if the quantities have increased your local store has received new stock of either the Stormtrooper Mimban figure or Wave 18. When the quantities do increase its possible that the new figures will either be on the pegs or on stock pallets that night in the toy department.
Hope this helps.