I don't think you will find the female half. Those are obsolete; you can't even get them at the electrical supply store; not made anymore. They are still around but the ones I've seen have been in poor condition and dangerous.
A lot has changed in standards since 1972. There are a couple options, like changing it to a pull-out cord that runs 30 amps in, but that requires having the space for the cord to retract inside and store...but not to convolute the situation, the best and SAFEST bet is changing that inlet.
If you are not comfortable doing it yourself, look up an electrician. It is not a huge job to install this and would not cost very much at all for the peace of knowing it is done right.