Depending on how ovalized is, the paint solution could work.

This is what I would do ok? Since the headset works by compression this could work just fine.

Use jbweld and add some material were is needed, sand the tube 1st to bare metal to get good adhesion. SO add the putty, sand it really well... then get some car paint, any color will do or maybe hmm... tamiya spray paint. put a few coats of that paint inside of the headtube obviously. Let it sit for 2 days, meanwhile measure it ok? If you are kind'a ok in the size just go to the lbs and ask them to ream it to specs.

The putty will be in place maybe forever and since it will work compressed it wont crack or anything.

My 2 cents.