I think the handle is actually off a 'rescue saw' big like that so a fireman can start the saw with gloves on. Lots of saw racers use them to make sure they don't blow the race. You can buy them from almost any on the manufacturers, in the 'service 'variations' part of the IPL.
The ones I like are stihl 460 rescue saw handles. Put one on my dad's 3300 as he has gotten older and the oem handle was hurting his hand on starts. I used them everywhere for racing or higher psi saws. Jacked some of them way up for cold start racing.
The 3300 my dad bought new, that I put a rescue handle on. This made my dads saw still startable for him. 21 years of use and still going.
Just make sure those high cube saws don't rip your shoulder out instead of rip the small starter handle out of your hand when they "snap back".