Hello Nicholas,
First of all, there is no such thing as ‘DSLR grain,’ for grain only pertains to film as opposed to digital footage that can only have noise (though various types of it).
Recreating grain and/or noise can be done in a number of ways depending on the budget and the required result. For a DSLR, the most accurate and not so costly solution is just to shoot a 50% grey card with the very same DSLR tuned to the very same aperture/shutter/ISO settings. If lit up properly, the resulting video can be used in AE on an upper layer set to Overlay or Soft Light blending mode.
However, many DSLR-shooters look for something a bit different: they would normally remove noise from their footage and then try to recreate film grain to get an extra cine-like look. This can be done either by built-in AE effects (cheap and fast but not optimal quality-wise) or by applying real film grain scans in exactly the same way as described above. You can buy full size (or download free previews) real film scans from companies like CineGrain, or google for some free samples.