I lost and replaced the center caps on the wheels several times. They are made of cheap plastic with micky mouse clips to hold them on.
Finally I decided the cost wasn't worth it and removed them all and run without now and it works just fine. The last ones I purchased were around $25 each plus shipping.
Id have to look, but may have a couple good caps in the garage....I know I have several that broke and won't stay on.
My XT-276 uses the same wheels as you have in the picture - black wheel with the 'chrome' double stripe.
The size of the center caps have to match the diameter of the wheel. That is 14" wheel center caps and 15" wheel center caps are different and will not interchance.