I suggest only removing a couple of spokes, to measure, before going further. Unless one already knows how to relace a wheel from separate parts it's far easier to just replace one spoke at a time to maintain the lacing pattern and handle the floppy partially apart wheel at the same time.

A spoke from each side, each hub flange, can be brought to a shop or coop and any measurement errors eliminated by direct comparison. On the rear wheels these bikes use there's generally a 2mm difference in length between the two sides of the built up wheel.

Where are the OEM spokes broken? At the hub/J bend, at the threaded end or somewhere in between? One trick to check the rim's untensioned condition is to relax all the spoke tensions about the same amount. As the spoke tensions decrease the more the rim will seek it's unstressed shape. By spinning the wheel one can watch the rim edges for any localized wobble of flat spots. A rim that is already flat and round will true up quicker and last longer Or another way, if the rim isn't pretty straight and round with essentially zero spoke tension the wheel will never last as long and one might not even be able to true out any wobbles. Andy

The reason why I ask about where along the spoke the breaks are is that there have been batches of badly made raw spoke stock. In the 1990s the LBS world saw thousands of lower cost bike wheels with stainless steel spokes that would form an "inclusion" or other issue that made that spot ultra brittle. This problem was on many different brands and there was little reason to why one bike suffered but the next one on the production line didn't. If your spokes are broken along their mid points look for small blackish spots on the spokes for possible future problems. When this problem was first noticed (and this was long before the interweb was what it is today, so information spread by word of mouth or in monthly industry publications. We initially just replaced a few of these breaking spokes but soon began to see returns with more broken spokes so we would just replace the complete wheel (less time and cost VS respoking the entire OEM wheel). For some of these we got reimbursement from venders, sometimes the shop ate the cost and sometimes the customer did. Even years later I would sometimes still see these bad spoke problems with tell tale spots and breakage points. Andy