This won't be much help if you want to do it tomorrow, but I ordered my string from here
. I ordered the 1.2mm TAN string and it was a perfect match for the original.
They have a way of determining how much you need on that page, but I just went ahead and ordered the 300ft. roll. I knew I'd have to do more later. Sure enough, I've done 4 now and still have some string left. If your DW doesn't have a big needle to loan you, order theirs ($1) - makes it much easier.
Good luck! The 1st one is the toughest!