I bet someone has already done this but I haven't seen it yet so I figured I'd do it myself. I made an external which lets me send midi clock, start, stop and continue messages out of pd. This way I can sync an external drum-machine, sequencer, etc., to pd.
I've placed the code here: http://x37v.info/projects/puredata/midi_sync_out/code/midi_sync_out.tar.gz
I just wrote it in the last hour or so, and have tested it only with 1 drum machine.. I'm using ALSA for midi, if you're not you'll have to modify the Makefile (I couldn't figure out how to send midi bytes in a generic way as the sys_queuemidimess function is static).
It is a super simple external. I tried for a while to simply use the [midiout] object but I couldn't figure out how to get it to actually output anything. I looked at the pd source code, it looks like there is a little bit of code to send clock out messages but I don't think it is exposed to the user in any object... and I didn't see anything about start/stop/continue messages.
There is a help file which explains the functionality of the object and gives a really basic sync out solution.
Please tell me if this works for you, if this is redundant [encompassed by another project (which you could point me to)], etc.
Thanks, Alex