bwest- any Honda motorcycle dealer should have it on the shelf. I run Honda Pro (black bottles) 10w/40 and 20w/50 and have about 2000 hours between 2 Rotax 912 and 912S engines with no problems. The Honda Pro does have gearbox lubrication additives. I do run 100% 100LL AV-Gas so I can't use a full synthetic oil.

Also Kitfox Aircraft now carries the new AeroShell Sport Plus 4 oil that meets or exceeds all of the Rotax 4-stroke requirements. Page 40 of their parts catalog.
$86.00 a case of 12. I'm thinking of switching to AeroShell Sport Plus 4 after I run through my present inventory of Honda Pro oil.