I think you are meaning non prescription reading glasses that are sold over the counter. I have seen a few +.5 eyeglasses on Ebay, but in most stores it typically start at +1.0. If you need reading glasses, you'd better have an eye exam and get reading glasses that is specified on your prescription.
The lowest power for reading glasses is +0.25, but you can't get anything below a magnification of +1.00 in drugstores or malls, and those are usually hard to find. In most case you'll have to have them custom made.
In most cases, +0.25 reading glasses, +0.50 reading glasses and +0.75 reading glasses are all considered low power reading glasses. The problem is that you canâ€™t get anything below a magnification of +1.00 in drugstores or malls, and those are usually hard to find. Powers of +1.25, +1.50 and above are easy to find anywhere readers are sold.
Most drug stores have ready-made reasing glasses with less than +1.50 diopters. However, you can find few stores have +1.25 or +1.00 reading glasses. If you want to get the lowest power for reading glasses, like +0.25, +0.50 or +0.75, you can either order them online or you can go to an optical store to have them made.