Use the dealer lookup on the evinrude site. M whoever is a dealer should have it. If not u can buy online for less most likely. I buy from a dealer but the last time they did not have the correct lower unit lube. Tg they still handle xd 100. I will also say that gander mountain is an absolute ripoff. My dealer sells it for 40 somebucks a gallon. Gander was over 20dollars more.
I know its a different cat, but I have a Yamaha 2 stroke and no one here in bismarck carries their oil at a resonable price any more. I ended up finding a Yamaha rebuilding company called Hydrotec Marine and they shipped it to me for cheaper than I could get it anywhere.
You might also want to look at the Amsoil HP Marine. Check out their website, their oil is supposed to be compliant with the XD-100.