My question is this: How could I use a set of drum triggers to play sounds in a sequencer? I've never seen a set of drum triggers that send midi messages.
You have to have what is called a "Trigger to MIDI Interface" or a TMI.
Roland sells a 6 channel version (the TMC6) that has the fastest conversion time available.
Here's the link to Interstate Music's listing. They sell it for $240.
You can use an Alesis D4 or DM5 (which you can pick up used) but the conversion to MIDI time is slow; but as long as you are just doing "midtempo" material, you shouldn't have any problems with it.
Yamaha made one as well...I think it was called the "TG-33".