Tri-X in Diafine will get you the grain you want at a speed point of about 1000, give or take a little. You'll also get a reasonably good range of tonal values, making the negatives relatively easy to print. Despite what the label says, Diafine is not a fine grain developer in the true sense of the word. But because the negatives are not as contrasty as they would be had the film been pushed that much in a more conventional developer, the grain is not as readily apparent. To make the grain more apparent, printing with a bit more contrast can take up the slack. If that's not enough for you, then try one of the super speed films from Kodak (P3200 TMax), Ilford (Delta 3200). or Fuji (Neopan 1600). Of the three, Ilford's product offers the most pronounced grain that suggests the look of popcorn or golf balls. Nothing more exotic than D-76 is needed for any of these films. I would not suggest Rodinal if you want to exploit some speed from them.