If you can find someone to take them all, that may not be a bad way to go about it. Then you can get sexed chicks so you know (well, at least are fairly certain) you'll be getting pullets.
There's nothing wrong with keeping the pullet you have, but you'll want to keep the current one seperated from, but preferably within sight of, the new chicks until the chicks catch up a bit in size and maturity. That may or may not be what you want to do depending on your situation. If it's going to be an issue and you are not too attached to the current pullet, I would just try to get me 3-4 new pullet chicks and go from there. It's a bummer, but that's the downside of 'straight run' chicks if you only want a few and aren't in a position where you can/want to butcher the extra birds.