If you are replacing 3 I would strongly suggest relacing the wheel. Spoke wheels derive their strength by being under tension. They distribute their load equally. With that many spokes missing the load is no longer equally distributed and the remaining spokes have been unequally stressed. At a minimum, it will be hard to true your wheel. At worse, spokes will continue to fail. While you are at it, carefully inspect the rim for damage and roundness and replace if in doubt
I know it is easy for me to tell you to spend your hard earned cash and valuable time but this is one of those repairs you do not want to take risks with
TC
Wally