I have come across two excellent websites for printable airgun targets, both sites cover 14cm and 17cm target sizes ready to put into your pellet catchers and target holders, but the Shooting Skull Target site also covers A4 and also have some A3 targets.

The first site is:

Shooting Skull Targets - https://shootingskulltargets.wordpress.com/

This site is fantastic and covers everything from standard airgun targets to vintage airgun targets, carnival airgun targets, human themed targets, airgun game targets and they have just added some free benchrest targets.

Shooting skull targets also have an excellent free printable scope sighting target, which makes zeroing a breeze. Download it from here

All targets are free to download and use.

The second site is:

Printable Airgun Targets - https://printableairguntargets.wordpress.com/

This site also has loads of useful targets from your basic standard airgun targets ones to fun airgun targets and HFT airgun targets, Benchrest targets and many more.

Again all targets are free to download and use.