Counting drops is going to be about as exact as you are going to get realistically. If I am mixing paint for coloration that's the only way I do it since a small variance in proportion can make a noticeable difference in shades.
You can usually find items for measuring small quantities at pet supply stores. Aquariums frequently need small quantities of chemicals added, and pets need small quantities of medicines.
Syringes are handy if you can get your hands on one. Try and find one with a small diameter since that requires more volume to be noticeable on the scale. If you need a tighter scale, use a ruler that reads in 1/64 inches or millimeters. Since you are more concerned with the proportion than the actual volume, using an arbritray scale will work fine.