The spoke size varies with the rim and hub...all your wheels may use different spoke sizes.

If you can measure accurately from the the head at the hub right to the rim then add 3mm (1mm for rim thickness and 2mm for nipple head) or so that should give you a decent approximation of spoke length to order replacements to have on hand.

I would recommend childhood_dreams on eBay. If you put together and order for several spokes of each length you need Lee can fix you up I imagine since he cuts and threads to order. The spoke you measured is a 2.0mm or 14G spoke. Lee also has double butted 14/15/14 should you need them.