G'day kenny_t,
As AVB says, chasing OEM parts will be difficult - some are available from US suppliers, but postage is a killer there.
FWIW, you can download an IPL from https://www.leonschainsawpartsandrepair.com/parts-diagrams.html

Your best bet might be to try a 'universal fit' string head, that comes with several shaft adaptors. A search on eBay Oz for 'speed feed trimmer head' will find a few - the 3.75" size is correct for an 18cc trimmer.

You will first have to determine the diameter, pitch and hand [i.e. LH/RH] of the shaft thread, though.

If it is a left hand thread, it will likely be metric, and these are the easiest to find heads for.

Cheers,
Gadge

"ODK Mods can explain it to you, but they can't understand it for you..."

"Crazy can be medicated, ignorance can be educated - but there is no cure for stupid..."