Steering column choices

I don't know much about aftermarket stuff but there are some easy options as far as stock columns are concerned.

You did not say what year your dart is but I'm assuming it's after 70 because that's when the key was installed in the column.

You also did not say if you have power or manual steering and whether your shifter is on the floor or on the column.

There were minor differences between each year but basically the column from a 67-76 A body will physically bolt into any other a body with a couple of distinctions:

The manual steering column is longer with a different steering coupler.
The power steering column is shorter with a different coupler.

The ignition key was located in the column after 69. It was in the dash before 70.

With this basic knowledge if you have a 70 car with manual steering, you could make a 67 manual column fit with some minor rewiring.

Likewise if you have 70 power steering use a 67-69 power column.

If you have column shift, get that column from a 67-69. If it's floor shift you can get a 67-69 floor shift column (pricey) or modify the column shift to remove the shift handle and PRNDL plate..

All of the 67-76 columns are readily available used and I would expect them to be cheaper and easier than aftermarket.