A 1 lb. roll of .045" piano wire costs about $5-$6 and will make hundreds of those trigger return springs. Been working of my roll for maybe 2 decades now, and it was $4 back then.
Here's some on Ebay a bit more, if your local hardware store doesn't carry it.
https://www.ebay.com/itm/Piano-Music...vqoJ-n1UDANFKg