My Forsetner bits are made by Dewalt and they do make an extension bar for te bits.
I can't give a link at the moment as I am at work and shouldn't be looking in here.
They are for larger diameter holes from 15mm up to 98 mm or there about.
Vinny does extra long drill drill bits at the Turners Workshop maybe not on his site but email him for details.
I have 7mm to 13mm in long length approx 180mm.
What diameter are you after?