Many of the items respawn in Glover Mallory's secret room in his basement. I don't know why you guys think, but in my mind his dialogue indicates that he wouldn't restock it (see below).
"Help yourself to whatever you like inside. I won't be using it anymore."
I noticed that the developers removed the respawn flag on the three dummy potions and the dummy sword. Strangely though, they didn't remove it on the dummy shield. This inconsistency makes me wonder if they started the process of removing respawn flags and never finished.
References:
040355C5, 0403ABE2, 0403BF4C, 0403BF4D, 0403BF4E, 0403BF4F, 0403BF50, 0403BF51, 0403BF52, 0403BF53, 0403BF54, 0403BF55, 0403BF56, 0403BF57, 0403BF58, 0403BF59, 0403BF5A, 0403BF5B, 0403BF5C, 0403BF5D, 0403BF5E, 0403BF5F, 0403BF60, 0403BF61, 0403BF62, 0403BF63, 0403BF64, 0403BF65, 0403BF66, 0403BF67, 0403BF68, 0403BF69, 0403BF6A, 0403BF6B, 0403BF6C, 0403BF70, 0403BF71, 0403BF73, 0403BF74, 0403BF75, 0403CF18, 0403CF19, 0403CF1A
I've attached a file to this ticket so that you can look over the items in question more quickly if you want to.

Attached Files:
MallorySecretRoom.esp