what engines are making successful aero engine conversions?

I'm in Western Australia. locally our supplies of VW engines seem to
have dried up. Even BMW motor cycle engines seem to have dried up.
what other currently available engines have been successfully used in
aircraft?

the engine problem seems to provide the most unsolvable dilema when
attempting to build a small aircraft. I'd hate to think that the
prospect of engine conversions was passing.

Stealth Pilot