Most seed traders that send seeds to places that are not import friendly tape their seed packs inside a greetings card or to a couple cardboard pieces and send them in a regular envelope.
A lot of seeds get through that way.
You might get some crushed seeds but enough will make it through to sprout.
I get seeds from all over the world and mostly use bubble envelopes marked Garden collectables-no value.All but a couple made it to the person I sent it to.
I've got over 4oo varieties of pepper seeds from trades and seed companies all over the place.
I also have some Cancun Habanero seeds that are well over 5yrs. old that sprout just fine.if kept dry and at room temp. they seem to last for longer than people think.

To get seed into australia is easy. Just have to label the envelope "Chilli Seeds" on the outside. The seeds should be in a clear plastic bag with a label of the variety and species name Eg. Capsicum chinense "Habanero". There should be no dried pepper flesh in with the seeds. All seeds sent to me have been recieved and some envelopes have been opened and taped back up with yellow "opened by quarantine" tape.

I'm anxious to see if any of my old seeds have survived. They did endure 2 summers with extended heat waves... not sure fingers crossed.

Always open to donations to start up again though .... lol

Update:

None of the pepper seeds germinated. However some Marglobe tomatoes sprouted. None of the other tomatoes sprouted though. I haven't lost hope completely, I'll replant more pepper seeds because the planted seeds are hardly likely to sprout now.

I have made dozens of trades with people in many countries and have never lost a shipment. My first shipment to Australia was held up because the baggies were not labeled with species but no problems since then. I use 5 x 7 bubble envelopes and don't write anything on them--less than 1 ounce does not require a customs slip. I got crushed seeds the other day from seeds not in a padded envelope. Please don't do that.

john