The good news is you can make a paste and blend spices with a coffee grinder, blender, or spice mill. The bad news (if it could be considered that) is you'll need to double, triple, or possible more, most recipes in order to ensure they reach the blades and blend properly.
But hey, life is life, so if you don't have the time nor inclination to hand pound pastes then eff it. There are alternatives. It just means more curry paste to hand for quick weeknight meals.
Methods of pounding pastes:
Spice Mill: If you want to make larger batches of paste, a spice mill or coffee grinder will work. Keep in mind you may need add water in order to keep the blades in contact with the paste, which will in turn dilute the end product. The alternative, as I mentioned above, is to increase the recipe. I recommend this over water any day.
Do not ever let anyone tell you that you can't make curry pastes without a mortar and pestle. If you've been using a spice grinder with success and are happy with that method, fine, but if you enjoy making your own pastes then I'd recommend an upgrade to a granite mortar and pestle.
Granite mortar and pestle: The process of pounding herbs and spices in a mortar and pestle supposedly extracts more flavour than any grinding method, so ideally the granite vessel will be your first choice for curry paste making. Smaller batches of paste can easily be made without water or oil dilution, and plus it's fun and a bit of a workout.
Maybe I will start posting curry paste exercise times to social media so everyone can know since everyone cares so much about other people's exercise regimes. Please let me know if you are aware of an app that tracks distance and GPS with regard to kitchen workouts.
Anyway. Look for a large, weighty model with at least a 6 inch opening and 6 inch depth. Pounding pastes lends itself to a lot of food-flinging, so the depth is important to keep those pesky ingredients from escaping. Don't get marble (it's too fragile for what it takes to make pastes). If you can take a car to collect your granite mortar, or order it by post, I highly recommend you do so. They weigh about 95 trillion tonnes.
Clay and wood mortar and pestle: Not as versatile as the granite mortar and pestle, the clay mortar and wood pestle are used only for simple preparations that do not take a lot of body and force (they aren't the power machines of granite make) and are used in making the popular Thai papaya salad som tam (and are suitable lighter dips and spread).
Blender: Sometimes I cheat and use a blender or liquidiser if I am making a boiled curry (e.g. sour or jungle curry). Rather than pound the paste and add it to liquid, I will add the liquid and all of the paste ingredients, finely cut, and liquidise them. This is a cheater method that saves time and works for after work meals and lazy days. This method is inappropriate in any Thai recipe that instructs you to fry paste first, whether in oil or cracked coconut cream.