Door locks, trunk locks, ignition lock cylinders....

with a collection of trunk locks you can build a few that fit the collection of keys you have.
its a 1 sided key so the job decsribed below in 2) is easier

and they fit so much better in the hole cut in the panel
the space for the gasket is better and the slide in spring clip to mount it fits better
also check the little door for the key isn't stuck or missing
The chrome seems to last better if you live in a salt/rust/snow type place.

for ignition and doors

1) you can do the poor mans hack, get your chosen ignition lock and key. get a selection of door look barrels. fit the key in each to identify the pair with the least number of pins or sliders sticking out with the key inserted. hopefully just one or 2 out of the full complement of 5 or 6...
File down flat with the barrel any that stick out and check that the barrel with the key inserted turns in the lock body, and won't turn in the lock body when the key is removed...

Its a hack job, and many a locksmith will be spinning in their grave...BUT it works

2) dismantle all of your door locks and use the huge array of pins/sliders you now have to rebuild 2 or 4 lock barrels to fit the ignition keys you have. its wasteful, its time consuming. you may have to hammer/beat the cover that holds the springs in, back into shape to get the lock to stay together, but it works. You are taking advantage of the fact that they built all locks from a pick -n- mix of a finite number of pins/sliders therefore if you have a lot of them you should be able to match any original key to a lock by choosing the correct pin/sliders.

until the late 70s for some manufacturers if you have 12 -24 different keys for a specific model you could open just about every car with that lock

My own locks use flat sliders and a double sided key
rectangular shims of metal with a rectangular window in them that the key passes through
double sided key pushes these sliders up or down so they all align with the side of the lock barrel with the key in, and springs push them to the extreme of their travel sticking out the sides of the barrel when the key is out.

Thus my rebuild not only involved getting the sliders in the correct order, i needed the window to be in the correct place and that might mean getting the slider to be the correct way up as they can fit both ways

for this type i inserted my key.
sprayed a mist of red paint down the holes were the sliders went
you could probably use a thin scribe instead to mark the key
pulled out key
cleaned paint off lock barrel
mounted key horizontally, in my soldering vice, and slid on sliders to each red paint marker
the set that hung at the same height was nearly right
bit of fiddling with 2 similar sliders from my pile, in the mix, got me a lock that worked

second one, after much messing around and no luck, had one that stuck out just a bit so i did Hack no.1) on it

ignition and doors now all open with the same key.