Every default air vehicle should have at least 1 T-10 parachute in them.
The C-130J is probably the best as it has something like 30 parachutes.
To get an ammobox of these things, I think Ruck box has them? Or just make a custom one. Put down any ammo box and put this in it's init field:
clearMagazineCargo this; clearWeaponCargo this; this addWeaponCargo ["ACE_ParachutePack", 30]; this addWeaponCargo ["ACE_ParachuteRoundPack", 30];
That will turn the box into nothing but parachutes, 30 of each type.
Once you're on the ground you can even recover the parachute. Look around to see where it fell, walk over and use "Repack Parachute" option. A little progress bar will appear. As soon as the parachute disappears look around near you for the backpack on the ground and pick it up to recover the parachute.