12pcs Joysticks Pad Cover, Button Protectors Thumbstick Joysticks Pad Cover Case for Playstation Vita PSV https://www.amazon.com/dp/B01C6MXIU8/ref=cm_sw_r_cp_api_i_VCSCV3RYH809QPQ5V31Y

These are the ones - They also come in different colors on Amazon.

I bought this set that works well as I didnt wish to wait for any delays from China. https://www.amazon.com/gp/product/B01C6MXIU8 Sakura has different kits for different device color with flat sticks, some with buttons and frames . Several have recommended them and videos on youtube for install. https://www.etsy.com/listing/776687143/rg350-psx-flat-stick-frame-screen-and and black https://www.etsy.com/listing/771319614/rg350-psx-black-flat-stick-frame-screen

I just googled searched the full text and found these on Amazon.com

https://www.amazon.com/ElementDigital®-Joysticks-Protectors-Thumbstick-Playstation/dp/B01C6MXIU8/ref=sr_1_1?keywords=ps+vita+thumb+grips&qid=1674060871&sr=8-1

Didn't take me long to find.

https://www.amazon.com/gp/aw/d/B01C6MXIU8?psc=1&ref=ppx_pop_mob_b_asin_title

These are ones I see recommended. Several styles to choose from. They're a tight fit on the RP3 but they work.