Use the Mods (only Java Edition) If the official Capes are exclusive, the Mods like Optifine or Advanced Capes Mod can help you.

To get the Minecraft anniversary creeper cape on Java Edition, players needs to visit official 15th anniversary page on Minecraft website and scroll down to find the option to claim creeper cape ...

Capes can be applied from the launcher (Image via Mojang Studios) Once you have a cape redeemed, you will need to apply it to the skin you are using on Java Edition.