Bread Baking Stone around Montreal, Canada

Yes, the ice cubes would probably be enough to crack your stone.  Generally ceramics tolerate high temperatures but are not strong and won't stand large temperature differences.  Thermal shock is not good.  If you want to throw water on a 450°F piece of ceramic you will need something with a low temperature coefficient of expansion (TCE).  And if you want it cheap you will have to look around for the bottom of an old microwave oven. They are made of pyroceram and have good properties at elevated temperatures. The TCE is around 10E-6/°K and a close relative material is made into glass stove tops.  They are thin (~5mm) so won't have all of the properties of a clay tile or granite stone but might tolerate some water (not so sure about ice cubes).

My experience with large baking stones was that, having broken three of them, I gave up and bought unglazed 6"X6" unglazed quarry tiles.  They're very cheap.  I've yet to break one.  I don't know of a heavy stone material available for baking purposes that won't crack when you throw water (liquid or ice) onto it when it's already at bread baking temperature.

On the other hand, I think that you can get the same steam effect by baking your loaves in a well-heated Dutch oven.  Have you tried this already?  If not, it's the technique that gives the great crust to Jim Lahey's no-knead bread.  See videos about it you can find searching on Youtube and maybe even on this site.  Lahey also has a pretty decent cookbook.

Considering "where you are coming from", a cordierite stone of at least 1/2" in thickness(preferably a little more) will serve you well. I traveled exactly the same journey; ie, started using a "mass market pizza stone" which cracked soon after the rigors of being put to use for real bread baking. The cheaper stone actually served well, for years, for the occasional pizza.

I then bought a 5/8" cordierite stone from nybakers.com and it has taken every thing that I have trown at it, so far(3 yrs in Nov), being used multiple times per week, on end. This is what nybakers says about their cordierite stones:

"... Our cordierite baking stones will resist thermal shock (i.e., cracking when cold water hits a hot stone) to temperatures in excess of 2300°F/1250°C, and possess both superior heat conduction and heat retention properties..."

http://nybakers.com/index.php?main_page=page&id=3#bakingstone

All that said, I never intentionally throw water directly on the hot stone. However, I don't worry about incidental spray from above, or incidental splashes from below. I also never take the hot stone out of the oven(and set it on a cool surface) if I don't have to. In the same tone, I don't preheat the oven to 500º and then place the cold stone in there. I'm sure if you try to crack these stones, you will succeed. Just from perusing the web, I have seen images of commercial ovens with cracks in their stone decks.

So if you can't locate a cordierite stone locally(kitchen stores, pottery shops, etc), I'm sure you can find them on the web somewhere there.

Amazon Canada: If you search around there at amazon, there are many more. Reasonable prices and free shipping with minimum purchase(buy anything else you need-incidentals, etc- to reach minimum).

http://www.amazon.ca/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=cordierite+pizza+stone&x=0&y=0

I recommend a "kiln" stone from a pottery supplier like Sial in Laval:

http://www.sial-canada.com/produitsDetails.php?nProductId=619&nId=9&nSegId=4

Way better than anything you can buy in a kitchen store.