Is there TIM store in the Marco Polo airport or in the Venice Central Rail Station?
I don’t think so.
To find stores search the linked website below:
Enter
Select PROVINCIA: Venezia
COMUNE: Venezia
then click CERCA (search)
If memory serves, there’s one not too far from the Rialto Bridge.
Melissa is right: it is near Rialto.
I know there is none at VCE. There a a number of them. Just google TIM stores Venice.