You could start by going to Rider's Club and having a look. On Sathorn Soi12
Most other places are further out. Given your location maybe there is someone up Ratchapreuk. As that is now a popular motorbike route. Ducati has a showroom near the big traffic circle, so there maybe somewhere nearby.
If all you want is an oil change/adjustment type of service you may even get lucky at the Honda dealer on Sukhumvit 71, near Jusco. If not I am sure they will know somewhere.