The Spring Postcards event camp equipment & other shop items should stay in your shop to be available to purchase for usually around 7 days following the expiration date of the event.
If all of your Spring Postcards event camp equipment & other shop items have disappeared from your shop tab have you tried some basic fault finding techniques?
Have you tried completely shutting down your game & restarting it.... fully closing down....not just swiping it in to the background?
Have you tried clearing your cache, cookies, history, etc?
If none of these suggestions work..... take some screenshots of your shop tab.
Then contact Pixel support directly & provide them with your screenshots.
You can contact Pixel support directly via your game settings menu.
Remember to check your email spam/junk folder for replies.
Don't send multiple tickets in quick succession to Pixel support otherwise their spambot might eat them.