Local hobby shop. Two- and 3-pin connectors are frequently used for servo and battery connections (for electronics, not power) in models. If you want to convert a socket to a plug, just pull pins from a header and insert them into the socket. Headers are available with pins up to more than an inch in length. I would source one with pins a little longer than the most common variety. You can also make the plug using crimp-on pins. Berg is one brand, but there are several.
John