If you've been looking for a bird leash or a bird harness for a small bird like those listed below, you're in luck! While not an actual corded or nylon style leash with metal buckles that is available for a larger bird, the Petite and Extra Small Avian Fashions Bird Diaper in Petite and Extra Small is available with an optional leash. It is the only option - at the time of this writing - that works as a bird leash for extra small pet birds.
I've looked high and low for an extra small or petite bird leash so that I can take my precious parrotlet, Mika, outside safely. Since I work in Bird Supplies, though, I've realized that it is probably impossible to find small yet tough cordage that one can sew attachment hardware on that would actually be comfortable and reliable for our very small pet birds.
Green Cheek Conures
But, the optional leash adds a whole new dimension to the innovative Bird Diaper by allowing you to take your bird outside for supervised walks, knowing that a wristlet style, removable leash will keep your bird safer. The removable leash attaches with a 1" wide Velcro strip. This short leash allows your very small pet bird to enjoy the benefits of sunshine and all of the enrichment that the outdoors has to offer.
Get your bird used to wearing the Bird Diaper with Leash Attachment in the house and learn how your bird reacts when it is startled prior to taking it outside. That way, should your bird become startled outside, you can quickly hold it close and allow both you and it to feel safe.