Something like this might work:
Should be an easy fix
You could go either route. Single piece stems are still available new. I recently changed over my single piece stem on my Cannondale R-800 to a two piece. When I looked, there are plenty of single piece stems out there. Probably cheaper to go the single piece route, but I really haven't priced it out in a bit.
Glad to hear your "mishap" took place off from a start and not somewhere in the 50 mile ride. Have a great day!
I think by "two-piece" you mean threadless stems, which are clamped directly to the fork, instead of inserted into the fork and held using an expander bolt. In order to use a threadless stem with your bike, you will need a threadless adapter, which are pretty easy to find and pretty cheap, but look kinda ugly, at least to some. Either that or a new fork, but 1" threadless forks are getting harder to find and there's probably no need for it. I would just go for a new threaded stem, personally, like the one that broke. It looks like the welds failed, though I have never seen that happen like that. You can get a Nitto stem for around $60 or less if you look: http://www.jensonusa.com/store/product/ST308B01-Nitto+Dynamic+Stem....
The disadvantages being that they don't have the bolt-on handlebar clamp, so you will need to unwrap/disconnect one side of your bars to install it. Also, they only come in silver, but they are very strong. There's also the Profile model still made, which has the bolt-on clamp, comes in black and is available to match the angle and length of your previous stem. Also cheaper than the Nitto:
Hope this helps.
I am glad you didn't get hurt. That looks like it could have been really nasty had it happened at the wrong place and time -and most places are the wrong place for a stem to break. Having it happen even when one is alone on the road can still turn into a mouthful of teeth missing!
Your LBS should be able to source a replacement part for you. I would guess (don't quote me here) that this is a standard 1" stem with a quill size of 25.4mm and a bar size of 23.8 mm. Amazon has a ton of them. Find one with the same rise and reach as what you have now. A "pop-top" type stem will be easier to install as you wont have to remove the brake and tape on one side to slide it in.
Or you can get a quill stem adapter and go with a threadless-type stem if that is what you want. Either way is OK but I think that the adapter + threadless stem route will probably cost you more money in the end as you will be buying two things. Amazon has some decent alloy stems for around $20.
Really lucky. It was probably cracked for some time. A good reminder for folks to look things over occaisonally, especially near tube junctions and welds.
Lots of people don't like the looks of a quill adapter with a threadless stem, but it does give you a lot more fit flexibility than sticking with a 1 piece quill stem. If you don't need the adjustment that they offer, there's no reason not to replace it with another quill stem like you had. Steel is an option, but I wouldn't think it's necessary. Salsa and Nitto both made/make good steel ones.
I would send the broken stem back to Deda, and see what they say. If there was a problem, they will appreciate knowing about it. They may even offer some compensation.