One thing you can do is to shoot with a wider angle lens or from farther away and then enlarge the snot out of it when printing. That will give you some grain.
Do you have a polarizing filter? I know you say you only have and ND filter, but many people don't think of a polarizer as being a ND filter on its own. That will cost you two stops worth of light. The polarizer combined with your ND might do the trick.
As far as devs go. Yes, Dektol will give you grain, so will Rodinol. I wouldn't go D-76; too much sulfite to reduce grain unless you went 1+3 with it, but I would still prefer Dektol or Rodinal.