i searched "Brickheadz Eyes" in Google. The first search result returns the Bricklink page which has the Bricklink part number 98138pb072. Search for this in Mecabricks. It will turn up 3 different colors of eyes.

Or use Brickset, search for a model and look at the parts list as a table. When you find the part, look for the Design Number. This is different from the number in the back of the book and you will probably never find a matching part on Mecabricks using that back of the instruction book number.

There are many other ways to find these numbers, but these are two ways.

Now, on to the way you searched for the part... I'm not sure what was going on when you searched, but if I click on Plates-Flat Tiles in the Workshop, the 24th option is a round 1x1 tile numbered 98138. (I do have to scroll down to get to the part.) It has a [+] in the top right corner of the icon. This means that there are more versions of this part if you click on the [+]. When you click that, it should load a group of decorated parts. When I clicked on the [+], it loaded 50 parts. Scrolling down, I can see both a black (98138d16) and a green (98138d36) eye. Is this what you are doing as well?

Found it Thank you so much really appreciate it also can you buy things you make

Here's some info:
https://www.mecabricks.com/en/forum/topic/771