Post implants 10+ years - Developed what feels like little tiny pebbles right underneath the skin. What could these be?

That is an interesting question.... I wish you had posted a picture. It is very hard to know what you are seeing and feeling, without seeing and feeling.
I'm guessing that you are referring to Montgomery Glands. Most women have 10-40 little bumps of their areola, around their nipple. These are tiny glands beneath the skin, some are larger than others that serve 2 purposes. 1) they secrete oil to keep the areolar skin soft.
2) They also release a very faint odor that draws a newborn to the mother nipple, helping them to latch on. The more Montgomery Glands, the faster a newborn will latch on.
I do not know if this is what you are feeling in your situation. It may be, but it is still worth being checked by a breast specialist. If it is not this, then maybe a biopsy might be the next option.
Good luck to you

Most women have 6 to 12 glands on their areola that secrete oily secretions that help stimulate newborn babies to suck milk.
The glands can occasionally get plugged up and can have buildup inside of them.
This is by far the most common scenario.
There are also rare forms of breast cancer that can form in this tissue. I suggest you get an evaluated by your primary care doctor.
. I suggest you get evaluated by your primary care doctor.
Best,
Mats Hagstrom, MD.