I am not 100% sure but I had my wife's 1997 Djebel 200 in bits yesterday. (Clutch sticking badly from corroded steel discs , the poor bike lived on a wine farm before we recently rescued it :-)
It's a 14mm thread and afaik all 14mm Suzuki bike sump plugs are M14x1.25.
You can get a short M14x1.25 bolt from the next fastener shop. Get it cut to size (some 12mm thread length) on a lathe or if you are desperate DIY with a hacksaw. Make sure the thread is rolled all the way to the head so that the plug goes in all the way and seals (with a new aluminium crush washer, replace every time you change oil, costs only little but keeps the sump plug where it belongs).
You can also try automotive dealers or bike shops. Many sell aftermarket sump plugs with little magnets which are supposed to fish for broken intestines of your engine.
Just be careful not to end up with a M14x1.5 plug which is used for Yamahas and cars. It will go into the thread a little bit and if you force it further you'll mess up the sump plug thread in the engine.
A little favour in return: What is the manufacturers model code in your bikes VIN? I am trying to source an original workshop manual for the Djebel 200(SH42A) until now without any success as I could not find out where the Djebel was officially sold (not here in South Africa). Might havebeen a Japan only model = only japanese manuals, shock!
Knowing that the DR200SE is near identical to our Djebel (except headlight, speedo and luggage carrier) I might get the manual for the SE as it should be easily available (200SE sold in US, some EU countries and even in South Africa). But I will need the model code, please!