Bear with me on this as this is going to sound contradictory...
You will not find a chinchilla without a bar in its genotype. Chinchillas are an agouti species - meaning each individual hair has more than one color on it (tip, bar, and underfur in the case of chins). At this time, there is no mutation in chinchillas to make them non-agouti, meaning every individual hair would be one solid color.
There are mutations, however, that mask the bar. The white series of mutations masks the bar, because either pigment production or pigment attachment is inhibited, thus you cannot determine the width of the bar, but genetically it's still there. Some of the ebony mutations also mask the bar, because they increase the amount of pigment production and/or its distribution. You have to have the right ebony mutation(s) and the right accumulation of it in order to mask the bar, but again, genetically, the bar is still there. I'd have to get some fur samples, but I think the black mutant factor (TOV) in combination with veiling genetics also masks the bar, but only within the veiling. The bar is still visible along the sides.
Since the bar is present in the genotype of all chinchillas, you can't select for or against it. You can, however, select for its width (thinner bar/longer tip is generally preferred, as this would be a darker phase animal) and its color (white, off-white or yellow/cream (undesired)).
The beige series of mutations affect the size (larger), shape (irregular), and number (decreased) of pigment granules, including in the eye, and dilutes the overall appearance of an animal from gray to beige (and a black animal to brown).
In order to get a chocolate, you want to combine the right ebony mutation(s) so that you get a chin with increased pigment production and distribution to the point that every hair would be completely black and the bar masked - with a beige mutation so that the black is diluted to brown.
I don't work with ebony precisely because the genotype is indeterminate (i.e. you cannot tell which of the seven known ebony mutations you're working with), so I cannot tell you how to select your ebonies to produce the extra dark barless eb.