I've had to replace this and i've got the old unit out but i destroyed the bolt that holds it in place, it's a unique bolt and i'm wondering if it comes with when i buy the ignition lock housing.

It's under
1997 Mercedes Benz s320 long > steering > ignition lock housing
M5025-112574

If you destroyed the unique bolt then you may have resorted to excessive force because it sounds like the steering lock may have inadvertantly rotated to the anti-theft position. When the lock is in this state you are unable to remove the bolt from the housing because the steel slide(s) inside the lock are positioned in the grooves of the bolt.

Some technicians may cut the damaged steering lock out of the steering column using a sawzall.......... IMO

Other technicians resort to drilling a 1/4" hole in a predetermined area of the lock housing so they can slide the anti-theft plate(s) away from the steering shaft using a small pick or a small screwdriver. Moving the plate(s) will allow you to rotate the steering lock to position 1 so the special bolt can be extracted from the the top. Yes, you will need to order a new bolt........

Repair tip:
Remove the steering lock and the electrical switch as an assembly, DO NOT seperate these two items from each other inside the vehicle because the steering lock, more often than not, can be mistakenly rotated to the "anti-theft" position!