In reply to nutme:
No climbing gear shops in Venice.
You could try this:
http://www.decathlon.it/it/store?store_id=PS_IT_34
It's 15 mins from Treviso Sud motorway exit, which is on your way, and is open Sundays 10am to 8pm. Will also be your cheapest option bar none.
Also at 'Treviso Sud', you'll find this place literally 300 m from toll booth.
http://www.sportler.com/redazione/header/filiali/treviso
It's a big, modern sports shop with huge mountaineering section. There's also a big indoor climbing wall...no membership required...Just turn up & climb.
But here's the catch I'm afraid. This being Italy, it looks like they're closed Sundays and Monday mornings. Open Monday pm from 2.30pm
Post edited at 05:40