DC-DC converter topology
There are piezo "transformers" that do exactly what you suggest.  Their output current is usually very low.  I haven't ever looked at one in detail, so I'm not sure whether 500 &micro;A is doable or not.  One advantage is that they can have very high voltage step up ratios and be physically smaller than a normal magnetic transformer.

I've never used one, or even looked at a datasheet in any detail, so I can't help further.  Look around on a distributor site like Mouser to see what's available, then peruse some datasheets carefully to see what is possible and what usage restriction there are.

That all said, getting 65 V from 5 V doesn't require anything exotic.  Why not use a typical boost converter?