There are plenty of manufacturers but unless you find the ONE that made the glass for the pre3 and you happen to be on very friendly business terms with them I am afraid it would be much easier to just buy another phone.
Unfortunately this is one of the pitfalls of buying a discontinued/unreleased/EOL product.
I am sorry to hear you are having problems.
Definitely sounds like a manufacturing defect however, noone is going to back it up.
In this case since the glass is not part of the the display but only covering it perhaps you can continue to use the phone and hope one pops up for spare parts on ebay.
For now I have dropped some super glue on the ends of the crack that "might" hopefully keep it from spreading. Then I have ordered some screen protectors coming from UK that will hopefully keeps my finger safe from getting a nice cut running across the crack
And I like your idea of checking to see if any Pre3 will go on ebay for parts. Something to keep an eye for. Thanks for the advice.