The standard size grease gun at any automotive or hardware store, 95% of them are all the same. You might see a 'deluxe' model with a padded grip or something but they all work the same and they all leak equally as bad after a couple years. Go ahead and buy the flexible hose as well because it's a sure bet you'll have at least one or two fittings you won't be able to reach with the solid tube.
The mini size is cute and handy for extremely limited use, but the replacement cartridges cost as much as the full size grease tubes. You're also very limited in the type of grease you can buy for them. For suspension and other high pressure, low speed applications you want to use a moly grease (molybdenum).