a converter you say. where might one get his little shady hands on one of them ?
There are converters around for both directions. A high impedance setup requires the panel to provide power to the mic, so the converter for using a low impedance mic (which doesn't need powering) in a high impedance aircraft will power itself from the panel, and generally works ok. Using a high impedance mic in a low impedance aircraft requires an extra source of power (since the panel isn't expecting to supply any), so these converters usually include a battery (generally a 9V PP9).
The better option seems to be a low impedance mic with a low->high converter, but different aircraft react differently. Converters can cause issues with VOX, for example (e.g. line held constantly open, etc).
There are plenty of suppliers around the 'net who stock this sort of thing; plug 'aircraft impedance converter' into your favourite search engine.