Yes the 210mm Gyuto saya will fit this knife. You can find it here:http://www.chefknivestogo.com/sayas.html
They're great knives but you're right the corian scales are heavier than normal wood scales. My own experience is you get used to what you use all the time.
My general comment is this is one of the best western handled knives we sell on the site. Great steel, great handle that is super durable and won't shrink. Sharpens well and holds an edge well.
Glad you like that Moritaka. They're one of my favorite makers on the site. PS speaking of sayas my woodworker just made some sayas to fit the Moritaka.http://www.chefknivestogo.com/safortoandmo.html
These will fit the Moritaka and the Tojiro ITK Kiritsuke Gyuto.