If you cannot find shallots, the white part of green onions is an acceptable substitute. Not as good, to be sure, but better than other onions.
If you want nice looking shallots—as for a salad or something you are not going to cook long—nip the tip off and slice it with a sharp paring knife in parallel cuts about 1/8 inch apart. Rotate it 90 degrees and repeat. Then place it on a cutting board and slice it in 1/8 inch slices. This will result in “pretty” small, square pieces. If cooking with it, it’s faster to just chop it.
For most cooking, slice the white parts crosswise, then chop; slice the greens crosswise and add at the last minute. Cooking them for long will turn them into mush.
For a special effect, cut the green part into 3-4 inch lengths, then cut them lengthwise into ribbons. Use these strips to garnish salads or soups. They are especially attractive in clear soups.